Mammalian Pyruvate Kinase Hybrid Isozymes: Tissue Distribution and Physiological Significance JANET M. CARDENAS AND ROBERT D. DYSON Department of Biochemistry and Biophysics, Oregon State Uncuerszty, Corvallis, Oregon 97331

ABSTRACT The purpose of this study was to examine the pyruvate kinase isozymic patterns of a wide variety of tissues from rats and mice, particularly regarding hybrid isozymes. For these studies, we employed longer electrophoresis times than used in most earlier studies in order to improve the resolution of closely spaced bands. The tissue distributions of types K, L, and M pyruvate kinases were found to be approximately the same as those reported earlier for rats and other mammals. In addition, K-M hybrids could be detected in most tissues examined in relative quantities which differed from one tissue to another in the same organism, in corresponding tissues from different species, and within a single tissue during development. Hybrid isozymes containing type L subunits occur in only a few tissues of either the fetus or the adult of either animal. In earlier studies utilizing L-M hybrid isozymes produced in vitro, we showed t h a t t h e kinetic properties of a given subunit are profoundly affected by the nature of its neighbors within the tetramer (Dyson and Cardenas, "731 J. Biol. Chem., 248: 8482-8488). Based on these altered kinetic properties, we suggest t h a t there is little need for a n organism to suppress completely t h e gene activity for one subunit type of pyruvate kinase during the synthesis of larger quantities of a second subunit type. Mammalian tissues a r e known to contain at least three noninterconvertible homotetrameric forms of pyruvate kinase (Imamura and Tanaka, '72; Susor and Rutter, '68, '71; Susor, '70; Whittell e t al., '73; Ibsen and Trippet, '73; Carbonell e t al., '73; Farina e t al., '74; Cardenas e t al., '75a). These homotetrameric forms have been assumed to be products of different genes. Type K, or I(4, apparently t h e primordial form, is t h e main isozyme of embryos, rapidly growing hepatomas, and certain adult organs such as kidney (Imamura and Tanaka, '72; Farina e t al., '74). Type M, or M4, is the main isozyme of skeletal and cardiac muscle and of brain. Type L, or Llr is found in liver and, in lesser quantities, in kidney. Erythrocytes reportedly contain a fourth isozyme (Suzor and Rutter, '71; Imamura and Tanaka, '72; Whittell e t al., '73; Schapira e t al., '75; Faulkner and Jones, '75a,b; Miwa et al., '75). This latter isozyme may be converted via proteolytic action into type L (Nakashima, '74; Marie e t al., '77). J . EXP. ZOOL. (1978)204: 361-368

The three pyruvate kinase isozymes have markedly different kinetic properties. Type K has slightly sigmoidal kinetics with the substrate phosphoenolpyruvate (nH = 1.4-1.7). The kinetics of type L a r e more strongly sigmoidal (nH = 2.5-3.0) while type M has hyperbolic kinetics with this substrate. Rat types K and L pyruvate kinases are both activated by fructose 1,6-biphosphate and inhibited by Lalanine and L-phenylalanine (Ibsen and Trippet, '74; Imamura e t al., '72; Cardenas e t al., '75b; Llorente et al., '70; Stifel and Herman, '71; Carbonell e t al., '73; Jimenez de Asua et al., '71). These effects presumably are import a n t in regulating the catalytic activity of t h e isozymes under changing metabolic states of t h e organism. Type M has hyperbolic kinetics with its substrates under normal assay conditions and is mildly inhibited by L-phenylalanine; this inhibition is reversed by L-alanine or fructose 1,6-biphosphate (Jimenez de Asua e t al., '71; Carminatti e t al., '71; Kayne and Price, '73; Cardenas e t al., '75b).

361

362

J A N E T M. CARDENAS AND ROBERT D. DYSON

Isozyme hybrids have been observed in fetal and newborn tissue (Susor and Rutter, '71; Faulkner and Jones, '75b) and in some adult tissue. Osterman and Fritz ('74) found five bands of activity, probably members of a K-L set, in intestinal mucosa, and Ibsen e t al., ('74) report the presence of a n M,K hybrid in rat heart in addition to M, and small amounts of K,. However, t h e difficulty in separating M, and K, has generally made i t difficult to detect their hybrids. In previous studies of pyruvate kinase isozyme patterns, we found that K-M hybrids occur in all bovine tissues examined, except they do not occur in adult erythrocytes (Strandholm et al., '75, '76). The widespread presence of hybrid isozymes in bovine tissues prompted us to investigate the isozyme distributions in some other organisms using t h e same highresolution techniques t h a t we used in our earlier work. Our results, reported here, reveal K-M hybrids in many mature, as well as developing, tissues of both rats and mice. In addition, we find t h a t fetal bovine hemopoietic tissue, including fetal red blood cells, contain K-L hybrid isozymes. EXPERIMENTAL PROCEDURE

mM 8-mercaptoethanol; debris was removed by centrifugation a t 10,000 x g for 15 minutes at 0". Hemopoietic cells were isolated from fetal bovine liver using methods described by Dyson et al. ('77). Other tissues were homogenized using a motor-driven glass homogenizer and two to three volumes (vollwt) of 0.02 M tris HC1, 1 mM EDTA, 1 mM fructose, 1,6-biphosphate, 10 mM 8-mercaptoethanol, a t pH 7.5 a t room temperature. Insoluble debris was removed by centrifuging for 20 m i n u t e s at 12,000 x g and 0". The supernatant was dialyzed against the electrophoresis buffer (0.02 M tris HC1, pH 7.5 at room temperature, 0.5 M sucrose, 1 mM EDTA, 1 mM fructose, 1,6-biphosphate, and 10 mM j3-mercaptoethano11 for two to six hours. Enzyme assays were performed at 25" by the method of Bucher and Pfleiderer ('55) in a n assay medium containing 0.05 M imidazole HC1, 0.1 M KCl, 10 mM MgCl,, 2 mM ADP, 1 mM phosphoenolpyruvate, 0.16 mM NADH, and 5 units of lactate dehydrogenase. Electrophoresis was carried out using the method of Susor and Rutter ('71) and the electrophoresis buffer described above. Dialyzed solutions were diluted to nine units (micromoles/minute) of pyruvate kinase activity per milliliter if more concentrated or were spotted several times at the origin in order to achieve the equivalent of nine units per milliliter. Electrophoretic patterns were recorded using F-5 Kodabromide paper.

Substrates and lactate dehydrogenase were obtained from Sigma Chemical Company. Sucrose was special enzyme grade from Schwarz Mann. All common chemicals were of the highest quality available. Solutions were prepared using distilled, deionized water. Cellulose acetate strips and equipment were obRESULTS tained from the Gelman Instrument Co. Rats were from a local colony of Wistar oriShown in figures 1 and 2 are representative gin; mice were of Swiss-Webster origin; zymograms obtained with mouse and r a t tisbovine fetuses were obtained from a local sues, respectively. Given in figure 3 are t h e slaughterhouse immediately after t h e ani- patterns obtained with heart and skeletal mals were killed. Rats and mice were lightly muscle from developing rats. I t should be anesthesized with ether before removing tis- noted t h a t we previously determined that no sues, which were immediately put on ice. new electrophoretic forms are produced by our Blood samples were obtained from adult rats procedures, demonstrated by homogenizing and mice by heart puncture and from r a t and two tissues together and examining the remouse fetuses by bleeding after decapitation. sulting electrophotetic patterns (Tolle et al., Fetal bovine blood samples were obtained '76). Hence, the isozymic patterns shown here from the umbilical cord. EDTA, 1 mM final should reflect t h e actual patterns in vivo. I n concentration, was used as a n anticoagulant addition, Strandholm e t al. ('76) found t h a t for all blood samples. Red cells were collected the three bands evenly spaced between bovine by centrifugation (5000 x g for 5 minutes at K, and M, are K-M hybrids with the subunit 0"). The plasma and buffy coat were removed compositions K3M, KzMz,and KM3, while the and the red cells were washed twice by resus- three bands evenly spaced between bovine K, pension in saline containing 1 mM EDTA and and L, a r e t h e corresponding hybrids K3L, centrifuging as before. Cell lysis was accom- K2L2,and KL3.Thus we feel safe in concluding plished by placing the cells in 1 mM EDTA, 1 t h a t the intermediate bands of rat and mouse

PYRUVATE KINASE HYBRID ISOZYMES

363

Fig. 1 Pyruvate kinase isozymes of murine tissues. Tissue samples were prepared and analyzed as described in the experimental section. Electrophoresis was performed for 35 hours a t 200 v. As minor electrophoretic variations occurred from one run to another, all patterns were aligned using the K, band as a standard. The leftmost band is K,, while the main band in adult heart is M,. L, is the rightmost band, seen in adult liver. The heavy band of the red cell samples can be distinguished from the M, band by its slightly higher anodal mobility and by the fact t h a t it can be removed by chicken anti rat L antiserum (Cardenas, unpublished results).

Fig. 2 Pyruvate kinase isozymes of rat tissues. Tissue samples were prepared and analyzed as described in the experimental section. Electrophoresis was performed for 21 hours a t 200 v. As minor electrophoretic variations occurred from one run to another, all patterns were aligned using the K, band as a standard. The leftmost band in the zymograms is K, and the rightmost band of adult liver indicated the relative position of the L4 band. Note the presence of bands, determined by relative electrophoretic mobility to be K-M hybrids, that are particularly visible in bladder and t h e bronchial area of the lung.

tissues are isozymic hybrids and t h a t their subunit composition can be predicted from their mobilities relative to t h e parental homotetramers. Like bovine tissues, most, if not all, tissues examined from mice and r a t s appeared to synthesize at least small quantities of K-type subunits, as evidenced by the presence of & itself and/or K-containing hybrids. In agreement with previous work, red blood cells from adult

rats contain at least two bands, and three closely spaced bands are visible in fetal red blood cells. The same two anodally migrating bands seen in adult red blood cells can also be seen in spleen. Relative mobilities suggest t h a t these closely spaced bands of red blood cells and hemopoietic tissue are not isozymic hybrids involving type K subunits. The light K, band seen in both red blood cell samples shown here could be contributed by a small

364

J ANE T M. CARDENAS AND ROBERT D. DYSON

present a situation analogous to t h a t in rat liver (Dyson e t al., '77). Shown in figure 4 is the first clear evidence of K-L hybrids in hemopoietic tissue. Bovine tissues are particularly useful for these studies because of t h e large size of the fetus and because of the great differences in electrophoretic mobility between K-L and K-M hybrids. K-L hybrids a r e clearly seen in fetal bovine liver but may well be contributed by t h e hemopoietic cells rather than by hepatocytes. The reason for this assumption is t h e enrichment of the hybrid bands in hemopoietic cells prepared from fetal liver and the presence of the same set of bands in red blood cells and spleens of bovine fetuses. While type K subunits seem to be ubiquitous in mouse, rat, and bovine tissue, type M subunits are also widespread, particularly in bovine (Strandholm et al., '76) and mouse tissues. It is interesting to note that the same subunit types can generally be seen in the corresponding organ from all three mammals examined here, albeit at different isozymic ratios. For example, rat uterine tissue contains mainly K,, small quantities of K3M, and even smaller quantities of K,M,; neither KM3 nor M, could be detected in our zymograms. Mouse uteri also contain more K-type than Mtype subunits, although the difference is less marked and all five members of the hybrid set are easily detectable. By comparison, bovine Fig. 3 K-M hybrids of pyruvate kinase isozymes in deuteri appear to synthesize nearly equal quanveloping r a t heart and thigh muscle. Electrophoresis was tities of both subunit types. In the uteri of all performed for 21 hours a t 200 v and 0" using the mobility three animals, as well as in many other tisof K,, t he leftmost band, a s a standard. The other bands, in order of increasing anodal mobility, a re K,M, KIM2, sues, the relative quantities of isozymes KM,, and M,. Note t he differences in the timing of t h e among the members of the hybrid sets are conisozyzmic shifts in t he two tissues. sistent with random combinations of varying ratios of two subunit types. Isozymic differences clearly occur from one number of contaminating white cells, altissue to another in a single organ t h a t probathough we cannot rule out the presence of K, bly reflect functional differences. For inin the red cells themselves. Fetal mouse red blood cells may contain a stance, the lung tip of the adult r a t contains greater multiplicity of bands t h a t can be seen mainly K, and only a small amount of K3M, in fetal r a t cells (fig. 11, a s intermediate bands while the bronchial area of the lung contains can easily be seen between the K, band and appreciably more M-type subunits. Adult t h a t of adult erythrocytes. At least seven bladder also contains prominent K-M hybrids. bands could be identified in mid-trimester In both lung and bladder, the isozymic patmurine fetal livers (fig. 1). We have not yet terns a r e suggestive of some compartmenbeen able to identify the nature of these bands talization of subunit types among the cells of due to the similarity of mobilities of murine these tissues, as evidenced by the nonrandom L,, M4, and the erythrocyte isozyme(s1. The patterns of isozymic hybrids. Such compartmultiple bands in adult mouse liver probably mentalization also occurs in bovine heart consist of L, plus K-M hybrids, based on their (Strandholm e t al., '76) and in bovine kidney electrophoretic mobilities, and thus would (Cardenas and Richards, unpublished results).

365

PYRUVATE KINASE HYBRID ISOZYMES

Fig. 4 Electrophoretic patterns obtained with fetal bovine hemopoietic tissue. Electrophoresis was performed a t 250 v for four hours and 0" using methods described in the procedures section. The heavy bands toward the left side of the patterns are K,, and the white bands seen in many of the samples are due to hemoglobin. The notches just to the right of the hemoglobin bands denote the origins, while other notches near the right ends of the patterns are identifying marks used during electrophoresis. The K,L band is just to the right of, and is partially obscured by, the white-appearing hemoglobin band. The next three dark bands are K,L,, KL, and L,, respectively, in order of increasing anodal mobility. Note the greater prevalence of hybrid isozymes in samples from the 2-month versus the 5-month fetus, as well as the nearly absent band of K, in red blood cells from the 5-month fetus

K-M hybrids are prominent in skeletal muscle during development, in agreement with previous studies on rats (Susor and Rutter, '71; Whittell e t al., '73; Guguen-Guillouzo et al., '77) and guinea pigs (Faulkner and Jones, '75a). Likewise, we find t h e same K-M hybrids in developing heart, although the timing of t h e isozymic transitions are clearly different for the two tissues. As can be seen in figure 3, skeletal muscle from newborn rats already contains large quantities of Mq, while hearts

obtained from the same animals contain mainly K,M2 and K,M with only traces of M,. Hence, there appear to be definite differences between the two tissues in the timing and/or the signals t h a t determine their pyruvate kinase isozymic composition. DISCUSSION

The results reported here indicate the widespread occurrence of K-M hybrids of pyruvate kinase in r a t s and mice. K-M hybrids were pre-

366

JANET M. CARDENAS AND ROBERT D. DYSON

viously demonstrated in adult bovine tissues and in developing tissues of several mammals. These same K-M hybrids are shown in the present work to occur in varying quantities in many tissues of the adult rat and mouse, and K-M hybrids will probably prove to be a general phenomenon, a t least among mammals. Thus, apparently most mammalian tissues synthesize at least small quantities of both types K and M subunit types throughout t h e life of t h e animals, and the simultaneous synthesis of two subunit types in the same cell results in the formation of hybrid isozymes. While the overall distribution of types K, L, and M isozymes of pyruvate kinase appears to be similar from one mammal to another, definitive differences in the relative quantities of isozyme subunit types occur. Similarly, differences in electrophoretic mobilities of the isozymes are apparent from one mammal to another, yet, for each mammal, type L has the highest anodal mobility, and thus probably the greatest net negative change, followed by type M, and finally by type K. While K-M hybrids occur widely among mammalian tissues, K-L hybrids do occur, albeit much more rarely. Osterman and Fritz ('73) reported their presence in intestinal mucosa, and Strandholm et al. ('75, '76) found them in bovine kidney. In this paper, we demonstrate their presence in hemopoietic tissue and in red blood cells of bovine fetuses. However, in spite of earlier reports of K-L hybrids in rat liver (Tanaka e t a]., '671, a careful search by Dyson e t al. ('77) using high resolution electrophoretic techniques failed to find K-L hybrids in fetal, regenerating, or normal adult r a t liver, or in Novikoff hepatoma cells. Thus, in view of the generalized occurrence of K-M hybrids but the much more limited presence of type L and especially of type L-containing hybrids, expression of the gene for type L pyruvate kinase appears to be much more restrictively regulated than the genes for the other two isozymes. As of yet, no evidence for the occurrence of natural L-M hybrids has been obtained, presumably because a given cell never synthesizes these two subunit types simultaneously. In order to interpret the isozymic patterns, i t is import a n t to note t h a t studies on the reversible denaturation of pyruvate kinase isozymes in vitro show t h a t any two of the three subunit types can combine randomly to form fivemembered hybrid sets (Cardenas and Dyson, '73; Strandholm e t al., '76).

As indicated in t h e introduction, t h e three pyruvate kinase isozymes have quite different kinetic and control properties t h a t presumably allow them to fulfill optimally the metabolic requirements of t h e tissues in which they a r e found. One may then ask why so many cells simultaneously synthesize two subunit types, resulting in the widespread occurrence of hybrid isozymes. We suggest t h a t the answer has to do with the effect of each subunit type upon i t s neighbors within t h e tetramer. We base this assertion on studies with isolated L-M hybrid isozymes, where it was shown t h a t L3M was very similar to L, in i t s kinetic properties, while LM, closely resembles M, in its kinetic properties (Dyson and Cardenas, '73). Since t h e two homotetrameric isozymes, L, and M,, differ more from each other t h a n any other two forms of pyruvate kinase, i t appears safe to assume that we can extrapolate these results to the other hybrids of pyruvate kinase. Thus, we would expect that the properties of any 3 to 1 pyruvate kinase hybrid would closely resemble those of the homotetramer comprised solely of the majority subunit. I t follows t h a t if types K and M subunits are free to join with each other in a random way, a s demonstrated for t h e L-M set in vitro (Cardenas and Dyson, '731, one can make the following prediction: from binomial theory, a cell t h a t produces, for example, 10% type K subunits and 90% type M subunits will have a hybrid set comprised of 65.6 percent M,, 29.2% KM3, 4.86% KZM2,0.36% K3M, and 0.01% K,. About 95% of t h e total pyruvate kinase activity in such a cell will be of the M, type (i.e., the sum of M, and KM,). If 95% of the subunits were M,, t h e amount of M,-like activity rises to nearly 98% (81.5% and 16.2% for M,and KM3, respectively. Thus, there is onIy a small incentive to suppress completely the synthesis of the fetal-type subunit in cells where the kinetic properties of one of the two specialized enzymes are needed. Why the synthesis of type L subunits should be more tightly regulated than the synthesis of the other two subunit types remains unknown. Alternatively, t h e possibility exists t h a t type L pyruvate kinase could be compartmentalized in some way and thus not free to form isozymic hybrids. However, there is as yet no evidence t h a t any of the three pyruvate kinase isozymes are found anywhere in t h e cell except in t h e cytosol. In conclusion, what we have shown here is

PYRUVATE KINASE HYBRID ISOZYMES

the very widespread distribution of pyruvate kinase isozymes, especially K - M hybrids, among mammalian tissues, while K-L hybrids are seen in very few tissues. ACKNOWLEDGMENTS

The support by National I n s t i t u t e s of Health Research Grants AM-15645 and GM15715 is gratefully acknowledged. LITERATURE CITED Bucher, T., and G. Pfleiderer 1955 Pyruvate kinase from muscle. Methods Enzymol., 1: 435-440. Carbonell, J., J. E. Feliu, R. Marco and A. Sols 1973 Pyruvate kinase. Classes of regulatory isoenzymes in mammalian tissues. Eur. J. Biochem., 37: 148-156. Cardenas, J. M., and R. D. Dyson 1973 Bovine pyruvate kinases. 11. Purification of the liver isozyme and i t s hybridization with skeletal muscle pyruvate kinase. J. Biol. Chem., 248:6983-6944. Cardenas, J. M., R. D. Dyson and J. J. Strandholm 1975a Bovine and chicken pyruvate kinase isozymes. Intraspecies and interspecies hybrids. In: Isozymes: Molecular structure. C. Markert, ed. Academic Press, New York, pp. 523-541. Cardenas, J. M., J. J . Strandholm and J . M. Miller 1975h Effects of phenylalanine and alanine on the kinetics of bovine pyruvate kinase isozymes. Biochemistry, 14: 4041-4045. Carminatti, H., L. Jimenez de Asua, B. Leiderman and E. Rozengurt 1971 Allosteric properties of skeletal muscle pyruvate kinase. J . Biol. Chem., 246: 7284-7288. Dyson, R. D., and J. M. Cardenas 1973 Pyruvate kinases. 111. Hybrids of the liver and skeletal muscle isozymes. J. Biol. Chem., 248: 8482-8488. Dyson, R. D., J. M. Cardenas, T . C. Richards and M. E. Garnett 1977 Pyruvate kinase isozymes in fetal andregenerating liver. Biochim. Biophys. Acta, 481: 115-126. Farina, F. A,, J. B. Shatton, H. P . Morris and S. Weinhouse 1974 Isozymes of pyruvate kinase in liver and hepatomas of the rat. Cancer Research, 34: 1439-1446. Faulkner, A,, and C. T. Jones 1975a Pyruvate kinase isoenzymes in tissues of the developing guinea pig. Arch. Biochem. Biophys., 170: 228-241. 1975b Pyruvate kinase isoenzymes in tissues of the human fetus. FEBS Lett., 53: 167-169. Guguen-Guillouzo, C., M:F. Szajnert, J. Marie, D. Delain and F. Schapira 1977 Differentiation in uiuo and in uitro of pyruvate kinase isozymes in rat muscle. Biochimie, 59: 65-71. Ibsen, K. H., and E. Krueger 1973 Distribution of pyruvate kinase isozymes among r a t organs. Arch. Biochem. Biophys., 157: 509-513. Ibsen, K., and P. Trippet 1973 A comparison of kinetic parameters obtained with three major non-interconvertihle isozymes of r a t pyruvate kinase. Arch. Biochem. Biophys., 156: 730-744. 1974 Effects of amino acids on the kinetic properties of three noninterconvertible rat pyruvate kinases. Arch. Biochem. Biophys., 163: 570-580. Imamura, K., and T. Tanaka 1972 Multirnolecular forms of pyruvate kinase from rat and other mammalian tissues. J. Biochem. Tokyo, 71: 1043-1051. Imamura, K., K. Taniuchi andT. Tanaka 1972 Multimolecular forms of pyruvate kinase. 11. Purification of M,-type pyruvate kinase from Yoshida ascites hepatoma 130 cells

367

and comparative studies on the enzymological and immunological properties of the three types of pyruvate kinases L, M, and M2. J. Biochem. Tokyo, 72: 1001-1015. Jimenez de Asua, L., E. Rozengurt, J. J . DeValle and H. Carminatti 1971 Some kinetic differences between the M isoenzymes of pyruvate kinase from liver and muscle. Biochim. Biophys. Acta, 235: 326-334. Kayne, F. J . , and N. C. Price 1973 Amino acid effector binding to rabbit muscle pyruvate kinase. Arch. Biochem. Biophys., 259: 292-296. Llorente, P., R. Marco and A. Sols 1970 Regulation of liver pyruvate kinase and the P E P crossroads. Eur. J. Biochem., 13: 45-54. Marie, J., H. Garreau and A. Kahn 1977 Evidence for a postsynthetic proteolytic transformation of human erythrocyte pyruvate kinase into L-type enzyme. FEBS Lett., 78: 91-94. Miwa, S., K. Ariyoshi and K. Shinohara 1975 Physiological and pathological significance of human pyruvate kinase isozymes in normal and inherited variants with hemolytic anemia. In: Isozymes: Physiological Function. C. Markert, ed. Academic Press, New York, pp. 487-500. Nakashima, K. 1974 Further evidence of molecular alteration and aberration of erythrocyte pyruvate kinase. Clin. Chim. A,, 55: 245-254. Osterman, J., and P. J. Fritz 1974 Pyruvate kinase isozymes from rat intestinal mucosa. Characterization and the effect of fasting and refeeding. Biochemistry, 13: 1731-1736. Osterman, J., P. J. Fritz, and T. Wuntch 1973 Pyruvate kinase isozymes from rat tissues. Developmental studies. J. Biol. Chem., 248: 1011-1018. Schapira, F., A. Hatzfeld and A. Weber 1975 Resurgence of some fetal isozymes in hepatoma. In: Isozymes, Developmental Biology. C. Markert, ed. Academic Press, New York, pp. 987-1003. Stifel, F. B., and R. H. Herman 1971 Effect of L-histidine on human and r a t jejunal pyruvate kinase activity. Can. J. Biochem., 49: 1105-1116. Strandholm, J . J., J . M. Cardenas and R. D. Dyson 1975 Bovine pyruvate kinase isozymes: Distribution and response to phenylalanine and alanine. Fed. Proc., 34: 509 (Abstract). Strandholm, J. J., R. D. Dyson and J. M. Cardenas 1976 Bovine pyruvate kinase isozymes and hybrid isozymes. Electrophoretic studies and tissue distribution. Arch. Biochem. Biophys., 173: 125-131. Susor, W. A. 1970 Multiple forms of pyruvate kinase during fetal development of the rat. Fed. Proc., 29: 729 (Abstract). Susor, W. A,, and W. J. Rutter 1968 Some distinctlve prop erties of pyruvate kinase purified from r a t liver. Biochem. Biophys. Res. Commun., 30: 14-20. 1971 A method for the detection of pyruvate kinase, aldolase, and other pyridine nucleotide linked enzyme activities after electrophoresis. Anal. Biochem., 43: 147-155. Tanaka, T., Y. Harano, F. Sue, and H. Morimura 1967 Crystallization, cheracterization, and metabolic regulation of two types of pyruvate kinase isolated from r a t tissue. J. Biochem., Tokyo, 62: 71-91. Tolle, S. W., R. D. Dyson, R. W. Newburgh and J. M. Cardenas 1976 Pyruvate kinase isozymes in neurons, glia, neurohlastoma, and glioblastoma. J. Neurochem, 27: 1355-1360. Whittell, N. M., D. 0. Ng, K. Prabhakararao and R. S. Holmes 1973 A comparative electrophoretic analysis of mammalian pyruvate kinase isozymes. Comp. Biochem. Physiol., 468: 71-80.

Mammalian pyruvate kinase hybrid isozymes: tissue distribution and physiological significance.

Mammalian Pyruvate Kinase Hybrid Isozymes: Tissue Distribution and Physiological Significance JANET M. CARDENAS AND ROBERT D. DYSON Department of Bioc...
631KB Sizes 0 Downloads 0 Views