INT . J . RADIAT . BIOL .,
1977,
VOL .
31,
NO .
3, 2 5 7 -264
Interactions of alkyl sulphates with bovine-serum Albumin studied using eaq as a probe C . V . EADSFORTH, D . M . POWER and E . W . THOMAS Department of Chemistry and Applied Chemistry, University of Salford, Salford M5 4WT, England
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
and J . V . DAVIES Paterson Laboratories, Christie Hospital & Holt Radium Institute, Manchester M20 9 BX, England (Received 6 October 1976 ; accepted 17 January 1977)
The reactions of hydrated electrons produced during pulse radiolysis have been used to investigate the binding of a range of alkyl sulphates to bovine-serum albumin . Binding to ten high-affinity sites is detectable for all compounds (methyl, hexyl, octyl, decyl, and dodecyl sulphates) studied . Sodium dodecyl sulphate, in contrast to the other analogues, causes large increases in the reactivity of BSA as a result of further binding . Possible mechanisms for this increase are discussed .
1 . Introduction In a previous study (Eadsforth, Power, Thomas and Davies 1976) the reactions of (SCN)2 . - , produced during pulse radiolysis, were used to study the binding of a range of alkyl sulphates to serum albumins . (SCN)2 .- proved to be a useful probe for the interaction of alkyl sulphates with their ten or so highaffinity binding sites in the albumins . Human and bovine albumins, however, in common with most proteins, have the capacity to bind much larger amounts of alkyl sulphates . We now show that the reactions of e a q , produced by pulse radiolysis, facilitates a study of this high-stoichiometry binding mode . A sharp distinction can also be made between the various alkyl sulphates with respect to their effects on the albumin reactivity towards e aq . 2.
Materials and methods Purification of the various alkyl sulphates and bovine serum albumin BSA was carried out as described (Eadsforth et al . 1976) . The pulse radiolysis equipment (at the Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester) and techniques have been described (Keene 1964) . Solutions for pulse radiolysis were prepared in triply-distilled water, with pH adjustment using 1 M HC1 or 2 M NaOH as required . Oscilloscope traces for the disappearance of e a q at 650 nm, when expressed as pseudo first-order plots of log 10 absorbance against time (in µsec) enabled kl to be calculated . The dose used for rate measurements was 200 rad, and for transient spectra, 2000 rad . Each experimental point is the mean of three determinations . Difference spectra induced by alkyl sulphate binding were measured using matched quartz cells as described (Polet and Steinhardt 1968), and a Unicam SP . 1800 instrument.
258 3.
C . V. Eadsforth et al . Results
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The value obtained for the bimolecular rate-constant k2 for the reaction of BSA with eaq varied with the sample investigated . Thus, values of 1 . 4 and 2 . 6 x 10 10 M -1 sec -1 were obtained from figure 1 . All the alkyl sulphates studies had k 2 -10 6 M -1 sec -1 for reaction with e a q . This large difference in reactivity enabled acquistion of binding profiles, representing BSA reactivity as a function of the amount of alkyl sulphate bound .
Methyl
2 .5 r Hexyl
2 .0 1 .5 1 .0
Octyl
Decyl 1 .5 10 40 :1
80 :1
120, 1
160 1
200 : 1 400 :1
Molar Ratio Alkyl Sulphate : BSA
Figure 1 . Interaction of different chain length alkyl sulphates with bovine serum albumin (10 -5 M) . Profiles show the rate-constants for e aq - disappearance at various, detergent-albumin complexes at pH 6 . Profiles for methyl, hexyl, octyl, and decyl sulphates are shown in figure 1 All compounds give an - 50 per cent reactivity decrease at relatively low ligand protein ratios . Methyl and hexyl sulphates give a somewhat more gradual reactivity loss than octyl and decyl sulphates, minimal reactivity being reached at ligand : protein ratios of - 40 : 1 and '- 10 : 1, respectively . In no case is a further change in reactivity apparent . With SDS (figure 2) the binding profile is dramatically different . An initial decrease in reactivity (10 : 1 ratio) is followed by two subsequent increases in reactivity (particularly well-defined at pH 11) at ratios of 50 : 1 and 300 : 1 . A marked depression of the 410 nm band in the transient spectrum resulting from e aq attack on BSA occurs with increasing amounts of sodium dodecyl sulphate (SDS), the intensity being reduced to very low levels with ratios of 100 : 1 (figure 3) . Methyl, decyl, and octyl sulphates have little or no effect on this 410 nm transient .
Interactions of alkyl sulphates with bovine-serum albumin -
Iq x 10 'sec
259
,
8
7
6
5
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4
3
2
oco ~. b ml~
L I 100 :1
200 :1
300 :1 400 :1
500 :1
Molar Ratio SDS : BSA
Figure 2 . Interaction of sodium dodecyl sulphate with bovine serum albumin (10 -5 M) . Profiles a and b show the rate-constants for e aq - disappearance at various detergentalbumin complexes at pH 6 and 11, respectively .
OD x 10_3 SEC 241
21
18 Methyl 15
t Decyl
12
Octy l
6
3
• 100 :1 200 :1 300 :1 400 :1
Dod ecyl `• 500 :1
Molar Ratio Alkyl Sulphate : BSA
Figure 3 . 410 nm transient absorption readings of various alkyl sulphate-bovine serum albumin complexes in argon-saturated solutions containing 10 -3 M D-Glucose . Absorption readings taken 100 µsec after pulse, dose 200-400 rad . BSA concentration 10-5 M . Path length 2 . 5 cm . The effect of sodium chloride on the interactions of hexyl sulphate and SDS with BSA is shown in tables 1 and 2 . kl measurements are corrected for the presence of NaCl at the three concentrations (10 -3 , 10 -2 , 10 -1 M) used .
260
C . V. Eadsforth et al .
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C. V. Eadsforth et al .
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
Obviously, reversal or blockage of protein-ligand interaction by NaCl will lead to a closer correspondence between observed and expected k l values for a particular complex . Such a situation is observed with the 30 : 1 sodium hexyl sulphate : BSA mixture in the presence of 10 -1 M NaCl . Figure 4 shows U .V. difference spectra for BSA in the presence of the various ligands . These difference spectra are an index of changes in chromophore (mainly Trp and Tyr) exposure to bulk solvent as a result of ligand binding. The most significant perturbation is seen with SDS .
AA r 5
., y 0 .025
1 0 .050
0 .075
0 .100 I .,
0 .125 270
280
290
300
310
Wavelength (nm)
Figure 4 . Difference spectra of various alkyl sulphate-bovine serum albumin complexes at pH 7 .4 in tris buffer . In all solutions BSA concentration 5 x 10 -5 M, alkyl sulphate 5 x 10-3 M except (2) (2-5x10-1M) . Spectra : (1) and (2)=C12 ; (3) =C10 ; (4)=Cs ; (5)=C4 ; (6)=C2 ; (7)=C1 . 4.
Discussion
The hydrated electron does not show a marked selectivity for any one amino-acid side chain (see Adams, Baverstock, Cundall and Redpath 1973) . Thus His, Trp, Cys and e-NH 3 + groups of Lys show high reactivity, but several other residues show a moderate reactivity (Swallow 1973) . Also observed transients (e .g . the 410 nm band assigned to the R-S-S-R electron adduct) may not represent the initial sites of attack on the protein, but end-products of a series of electron-transfer reactions . Discussion of the present results is complicated by these two factors, but the following points are relevant : (a) All the alkyl sulphates studied reduce the reactivity of BSA by -50 per cent . Inflection points in the binding profiles (figure 1) indicate that the decrease in reactivity is due to occupancy of the ten high-affinity binding sites . Thus octyl and decyl sulphates show sharp inflection points at ligand : protein ratios of - 10 : 1, indicating strong stoichiometric binding . Methyl and hexyl sulphates obviously interact less strongly : their binding curves approximate to rectangular hyperbolae, indicating an equilibrium situation with a significant
Interactions of alkyl sulphates with bovine-serum albumin
263
amount of unbound ligand in solution . An approximate estimate of the binding constant may be made from such data, the amount of ligand required to reduce the reactivity of BSA by 50 per cent KD, a dissociation constant . From figure 1, this would correspond to about 1 .7 x 10 -4 M hexyl sulphate, in turn corresponding to an interaction energy of
- 5 . 26 K cal mole -1 .
A quoted value
(Tanford 1973) indicates an approximate affinity of - 6 K cal mole- ' for the hexyl sulphate-BSA interaction, based on equilibrium dialysis measurements .
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Although BSA is known to bind hexyl, octyl, and decyl sulphates in larger amounts than 10 mole - ' (Steinhardt and Reynolds 1969) no indication of changes in protein reactivity towards e q- are apparent (figure 1) . There are also no significant changes in the intensity of the 410 nm transient (figure 3) attributable to R-S-S-R anion . Presumably the overall conformation of BSA has not changed drastically as a result of high-stoichiometry binding of the above ligands . (b) The initial
- 50 per cent decrease in reactivity, observed with all the
alkyl sulphate analogues, may be interpreted in terms of the model we previously proposed for the ten high-affinity binding sites, i .e . that they are found in one locus in BSA . This locus is then postulated to be a significant point of attack by e a q , as well as (SCN) 2 •-.
Attack on the two Trp residues by e a q can only
be of minimal quantitative importance, since the final screening effect produced by methyl sulphate is similar to that of the bulkier ligand, decyl sulphate . We suggest that the reduction in reactivity results from screening of protonated e-amino groups (Lys) by electrostatic interactions with RSO4 .
That such
residues (presumably Lys) are quantitatively significant in the overall reactivity of BSA is indicated by the fact that k 2 at pH 6 (1 . 3 x 10 10 M -1 sec 1) is more All the alkyl sulphates than twice k2 measured at pH 11 (0 . 6 x 10 10 M -1 sec 1 ) . are thought to make this electrostatic interaction with BSA, with additional contributions to binding by hydrophobic interactions with the alkyl chains . These interactions only become significant when R > C6 . Thus the hexyl sulphate interaction, being more ` purely ' electrostatic, is more easily destroyed by salt than the SDS interaction, in which hydrophobic forces play a large part (tables 1 and 2) . (c) Paradoxically, the dramatic increases in reactivity observed with high SDS concentrations do not appear to be paralleled by increases in the 410 nm transient .
A priori, reactivity would be expected to decrease, since SDS
binding would increase the net negative charge on BSA thus tending to repel eaq, and also shield side-chains from attack by e aq .
It is also known that
the susceptibility of protein cystinyl residues to chemical attack (notably by low-molecular weight thiols) is not decreased but in fact facilitated by high concentrations of SDS . The massive binding of SDS, but not shorter chain analogues, is known to result in the destruction of tertiary protein structure as a result of polypeptide chain unfolding : this effect is well demonstrated in figure 4 . The radiation chemistry of proteins in the presence of SDS is now being closely studied in this laboratory .
ACKNOWLEDGMENT
This work was, in part, supported by grants from the Cancer Research Campaign and the Medical Research Council .
264
Interactions of alkyl sulphates with bovine-serum albumin
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Les reactions des electrons hydrates produites pendant la radiolyse de la solution aqueuse de KCNS, ont ete utilisees pour etudier les combinaisons d'une serie de sulphates alkyl sur le serum humain (HSA) et bovin (BSA) . On peut determiner environ 10 sites de haute affinite pour tous les composes etudies (sulphates de methyl, hexyl, octyl, decyl et dodecyl) . Contrairement aux sulphates analogues, les sulphates de sodium de dodecyl augmentent l'intensite de la reaction du serum bovin, ce qui est du a une combinaison supplementaire. Les mecanismes probables causant cette augmentation d'intensite font l'objet de discussion . Die Reaktionen hydratisierter Elektronen, die wahrend der Pulsradiolyse gebildet werden, wurden verwandt, um das Bindungsvermogen einer Reihe von Alkylsulfaten an Rinderserumalbumin zu untersuchen . Bei alien untersuchten Verbindungen (Methyl-, Hexyl-, Octyl-, Decyl-, and Dodecyl-Sulfat) konnte eine Bindung an zehn stark affine Stellen festgestellt werden . Im Gegensatz zu allen anderen Analogen verursachte Natriumdodecyl-Sulfat einen grolleren Anstieg der Reaktivitat des Rinderserumsalbumins, was auf weitere Bindungen zuruckgefuhrt wird . Mogliche Mechanismen fur diesen erhohten Anstieg werden diskutiert .
REFERENCES
G . E ., BAVERSTOCK, K . F ., CUNDALL, R . B ., and REDPATH, J . L ., 1973, Radiat . Res ., 54, 375 . EADSFORTH, C . V., POWER, D . M ., THOMAS, E . W ., and DAVIES, J . V., 1977, Int. Y. Radiat . Biol ., 30, 449 . KEENE, J . P ., 1964, Y. scient . Instrum., 41, 493 . POLET, H ., and STEINHARDT, J ., 1968, Biochemistry, 7, 1348 . STEINHARDT, J ., and REYNOLDS, J . A., 1969, Multiple Equilibria in Proteins (New York Academic Press) . SWALLOW, A . J ., 1973, Radiation Chemistry (London : Longmans), Chap . 10 . TANFORD, C ., 1973, The Hydrophobic Effect (New York : John Wiley), Chap . 15 . ADAMS,
1977,
VOL .
31,
NO .
3, 2 5 7 -264
Interactions of alkyl sulphates with bovine-serum Albumin studied using eaq as a probe C . V . EADSFORTH, D . M . POWER and E . W . THOMAS Department of Chemistry and Applied Chemistry, University of Salford, Salford M5 4WT, England
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
and J . V . DAVIES Paterson Laboratories, Christie Hospital & Holt Radium Institute, Manchester M20 9 BX, England (Received 6 October 1976 ; accepted 17 January 1977)
The reactions of hydrated electrons produced during pulse radiolysis have been used to investigate the binding of a range of alkyl sulphates to bovine-serum albumin . Binding to ten high-affinity sites is detectable for all compounds (methyl, hexyl, octyl, decyl, and dodecyl sulphates) studied . Sodium dodecyl sulphate, in contrast to the other analogues, causes large increases in the reactivity of BSA as a result of further binding . Possible mechanisms for this increase are discussed .
1 . Introduction In a previous study (Eadsforth, Power, Thomas and Davies 1976) the reactions of (SCN)2 . - , produced during pulse radiolysis, were used to study the binding of a range of alkyl sulphates to serum albumins . (SCN)2 .- proved to be a useful probe for the interaction of alkyl sulphates with their ten or so highaffinity binding sites in the albumins . Human and bovine albumins, however, in common with most proteins, have the capacity to bind much larger amounts of alkyl sulphates . We now show that the reactions of e a q , produced by pulse radiolysis, facilitates a study of this high-stoichiometry binding mode . A sharp distinction can also be made between the various alkyl sulphates with respect to their effects on the albumin reactivity towards e aq . 2.
Materials and methods Purification of the various alkyl sulphates and bovine serum albumin BSA was carried out as described (Eadsforth et al . 1976) . The pulse radiolysis equipment (at the Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester) and techniques have been described (Keene 1964) . Solutions for pulse radiolysis were prepared in triply-distilled water, with pH adjustment using 1 M HC1 or 2 M NaOH as required . Oscilloscope traces for the disappearance of e a q at 650 nm, when expressed as pseudo first-order plots of log 10 absorbance against time (in µsec) enabled kl to be calculated . The dose used for rate measurements was 200 rad, and for transient spectra, 2000 rad . Each experimental point is the mean of three determinations . Difference spectra induced by alkyl sulphate binding were measured using matched quartz cells as described (Polet and Steinhardt 1968), and a Unicam SP . 1800 instrument.
258 3.
C . V. Eadsforth et al . Results
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
The value obtained for the bimolecular rate-constant k2 for the reaction of BSA with eaq varied with the sample investigated . Thus, values of 1 . 4 and 2 . 6 x 10 10 M -1 sec -1 were obtained from figure 1 . All the alkyl sulphates studies had k 2 -10 6 M -1 sec -1 for reaction with e a q . This large difference in reactivity enabled acquistion of binding profiles, representing BSA reactivity as a function of the amount of alkyl sulphate bound .
Methyl
2 .5 r Hexyl
2 .0 1 .5 1 .0
Octyl
Decyl 1 .5 10 40 :1
80 :1
120, 1
160 1
200 : 1 400 :1
Molar Ratio Alkyl Sulphate : BSA
Figure 1 . Interaction of different chain length alkyl sulphates with bovine serum albumin (10 -5 M) . Profiles show the rate-constants for e aq - disappearance at various, detergent-albumin complexes at pH 6 . Profiles for methyl, hexyl, octyl, and decyl sulphates are shown in figure 1 All compounds give an - 50 per cent reactivity decrease at relatively low ligand protein ratios . Methyl and hexyl sulphates give a somewhat more gradual reactivity loss than octyl and decyl sulphates, minimal reactivity being reached at ligand : protein ratios of - 40 : 1 and '- 10 : 1, respectively . In no case is a further change in reactivity apparent . With SDS (figure 2) the binding profile is dramatically different . An initial decrease in reactivity (10 : 1 ratio) is followed by two subsequent increases in reactivity (particularly well-defined at pH 11) at ratios of 50 : 1 and 300 : 1 . A marked depression of the 410 nm band in the transient spectrum resulting from e aq attack on BSA occurs with increasing amounts of sodium dodecyl sulphate (SDS), the intensity being reduced to very low levels with ratios of 100 : 1 (figure 3) . Methyl, decyl, and octyl sulphates have little or no effect on this 410 nm transient .
Interactions of alkyl sulphates with bovine-serum albumin -
Iq x 10 'sec
259
,
8
7
6
5
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
4
3
2
oco ~. b ml~
L I 100 :1
200 :1
300 :1 400 :1
500 :1
Molar Ratio SDS : BSA
Figure 2 . Interaction of sodium dodecyl sulphate with bovine serum albumin (10 -5 M) . Profiles a and b show the rate-constants for e aq - disappearance at various detergentalbumin complexes at pH 6 and 11, respectively .
OD x 10_3 SEC 241
21
18 Methyl 15
t Decyl
12
Octy l
6
3
• 100 :1 200 :1 300 :1 400 :1
Dod ecyl `• 500 :1
Molar Ratio Alkyl Sulphate : BSA
Figure 3 . 410 nm transient absorption readings of various alkyl sulphate-bovine serum albumin complexes in argon-saturated solutions containing 10 -3 M D-Glucose . Absorption readings taken 100 µsec after pulse, dose 200-400 rad . BSA concentration 10-5 M . Path length 2 . 5 cm . The effect of sodium chloride on the interactions of hexyl sulphate and SDS with BSA is shown in tables 1 and 2 . kl measurements are corrected for the presence of NaCl at the three concentrations (10 -3 , 10 -2 , 10 -1 M) used .
260
C . V. Eadsforth et al .
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Interactions of alkyl sulphates with bovine-serum albumin
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Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
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261
26 2
C. V. Eadsforth et al .
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
Obviously, reversal or blockage of protein-ligand interaction by NaCl will lead to a closer correspondence between observed and expected k l values for a particular complex . Such a situation is observed with the 30 : 1 sodium hexyl sulphate : BSA mixture in the presence of 10 -1 M NaCl . Figure 4 shows U .V. difference spectra for BSA in the presence of the various ligands . These difference spectra are an index of changes in chromophore (mainly Trp and Tyr) exposure to bulk solvent as a result of ligand binding. The most significant perturbation is seen with SDS .
AA r 5
., y 0 .025
1 0 .050
0 .075
0 .100 I .,
0 .125 270
280
290
300
310
Wavelength (nm)
Figure 4 . Difference spectra of various alkyl sulphate-bovine serum albumin complexes at pH 7 .4 in tris buffer . In all solutions BSA concentration 5 x 10 -5 M, alkyl sulphate 5 x 10-3 M except (2) (2-5x10-1M) . Spectra : (1) and (2)=C12 ; (3) =C10 ; (4)=Cs ; (5)=C4 ; (6)=C2 ; (7)=C1 . 4.
Discussion
The hydrated electron does not show a marked selectivity for any one amino-acid side chain (see Adams, Baverstock, Cundall and Redpath 1973) . Thus His, Trp, Cys and e-NH 3 + groups of Lys show high reactivity, but several other residues show a moderate reactivity (Swallow 1973) . Also observed transients (e .g . the 410 nm band assigned to the R-S-S-R electron adduct) may not represent the initial sites of attack on the protein, but end-products of a series of electron-transfer reactions . Discussion of the present results is complicated by these two factors, but the following points are relevant : (a) All the alkyl sulphates studied reduce the reactivity of BSA by -50 per cent . Inflection points in the binding profiles (figure 1) indicate that the decrease in reactivity is due to occupancy of the ten high-affinity binding sites . Thus octyl and decyl sulphates show sharp inflection points at ligand : protein ratios of - 10 : 1, indicating strong stoichiometric binding . Methyl and hexyl sulphates obviously interact less strongly : their binding curves approximate to rectangular hyperbolae, indicating an equilibrium situation with a significant
Interactions of alkyl sulphates with bovine-serum albumin
263
amount of unbound ligand in solution . An approximate estimate of the binding constant may be made from such data, the amount of ligand required to reduce the reactivity of BSA by 50 per cent KD, a dissociation constant . From figure 1, this would correspond to about 1 .7 x 10 -4 M hexyl sulphate, in turn corresponding to an interaction energy of
- 5 . 26 K cal mole -1 .
A quoted value
(Tanford 1973) indicates an approximate affinity of - 6 K cal mole- ' for the hexyl sulphate-BSA interaction, based on equilibrium dialysis measurements .
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
Although BSA is known to bind hexyl, octyl, and decyl sulphates in larger amounts than 10 mole - ' (Steinhardt and Reynolds 1969) no indication of changes in protein reactivity towards e q- are apparent (figure 1) . There are also no significant changes in the intensity of the 410 nm transient (figure 3) attributable to R-S-S-R anion . Presumably the overall conformation of BSA has not changed drastically as a result of high-stoichiometry binding of the above ligands . (b) The initial
- 50 per cent decrease in reactivity, observed with all the
alkyl sulphate analogues, may be interpreted in terms of the model we previously proposed for the ten high-affinity binding sites, i .e . that they are found in one locus in BSA . This locus is then postulated to be a significant point of attack by e a q , as well as (SCN) 2 •-.
Attack on the two Trp residues by e a q can only
be of minimal quantitative importance, since the final screening effect produced by methyl sulphate is similar to that of the bulkier ligand, decyl sulphate . We suggest that the reduction in reactivity results from screening of protonated e-amino groups (Lys) by electrostatic interactions with RSO4 .
That such
residues (presumably Lys) are quantitatively significant in the overall reactivity of BSA is indicated by the fact that k 2 at pH 6 (1 . 3 x 10 10 M -1 sec 1) is more All the alkyl sulphates than twice k2 measured at pH 11 (0 . 6 x 10 10 M -1 sec 1 ) . are thought to make this electrostatic interaction with BSA, with additional contributions to binding by hydrophobic interactions with the alkyl chains . These interactions only become significant when R > C6 . Thus the hexyl sulphate interaction, being more ` purely ' electrostatic, is more easily destroyed by salt than the SDS interaction, in which hydrophobic forces play a large part (tables 1 and 2) . (c) Paradoxically, the dramatic increases in reactivity observed with high SDS concentrations do not appear to be paralleled by increases in the 410 nm transient .
A priori, reactivity would be expected to decrease, since SDS
binding would increase the net negative charge on BSA thus tending to repel eaq, and also shield side-chains from attack by e aq .
It is also known that
the susceptibility of protein cystinyl residues to chemical attack (notably by low-molecular weight thiols) is not decreased but in fact facilitated by high concentrations of SDS . The massive binding of SDS, but not shorter chain analogues, is known to result in the destruction of tertiary protein structure as a result of polypeptide chain unfolding : this effect is well demonstrated in figure 4 . The radiation chemistry of proteins in the presence of SDS is now being closely studied in this laboratory .
ACKNOWLEDGMENT
This work was, in part, supported by grants from the Cancer Research Campaign and the Medical Research Council .
264
Interactions of alkyl sulphates with bovine-serum albumin
Int J Radiat Biol Downloaded from informahealthcare.com by York University Libraries on 01/01/15 For personal use only.
Les reactions des electrons hydrates produites pendant la radiolyse de la solution aqueuse de KCNS, ont ete utilisees pour etudier les combinaisons d'une serie de sulphates alkyl sur le serum humain (HSA) et bovin (BSA) . On peut determiner environ 10 sites de haute affinite pour tous les composes etudies (sulphates de methyl, hexyl, octyl, decyl et dodecyl) . Contrairement aux sulphates analogues, les sulphates de sodium de dodecyl augmentent l'intensite de la reaction du serum bovin, ce qui est du a une combinaison supplementaire. Les mecanismes probables causant cette augmentation d'intensite font l'objet de discussion . Die Reaktionen hydratisierter Elektronen, die wahrend der Pulsradiolyse gebildet werden, wurden verwandt, um das Bindungsvermogen einer Reihe von Alkylsulfaten an Rinderserumalbumin zu untersuchen . Bei alien untersuchten Verbindungen (Methyl-, Hexyl-, Octyl-, Decyl-, and Dodecyl-Sulfat) konnte eine Bindung an zehn stark affine Stellen festgestellt werden . Im Gegensatz zu allen anderen Analogen verursachte Natriumdodecyl-Sulfat einen grolleren Anstieg der Reaktivitat des Rinderserumsalbumins, was auf weitere Bindungen zuruckgefuhrt wird . Mogliche Mechanismen fur diesen erhohten Anstieg werden diskutiert .
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