BIOCHEMICAL
Vol. 64, No. 2, 1975
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
THE /3-GAIACTOSIDASE-CATALYZED g-GALACTOSIDE
OF c-NITROPHENOL-B-
AT SUBZERO TEMPERATURES:
GAIACTOSYL-ENZYME
EVIDENCE FOR A
INTERMEDIATE
Anthony Division
HYDROLYSIS
L. Fink
of Natural
Santa
Cruz,
California
Received
April
2,1975
and Kim J.
Sciences,
Angelides
University
of California,
95064.
The reaction of fl-galactosidase (E. coli Kl2) with oenyl-/3-D-galactoside has been inves'figax over the tmrange=-t-25O to -30' using 50% aqueous dimethyl sulfoxide as solvent. At temperatures below -10' turnover becomes very slow and a burst of o-nitrophenol is observed. Such a burst indicates the existence of a galactosyl-enzyme intermediate whose breakdown is rate-limiting and provides a means of determining the active site normality. The Arrhenius plot for turnover is linear in the -25 to +25O range with Ea = 26 f 3 kcal/mole. The presence of the 50% DMSO had no effect on Km but caused a small decrease in kcat.
==T nltrop perature
/3-Galactosidase which
has been
K12 is a tetramer
from 5.
the
subject
of several
recent
concerning its mechanism of action, From H2 18 0 and other studies it is
clear
is
cleaved
hydrolysis
is
the
oxygen
in
the
methionine
the
as well
alcohol
Copyright AII rights
residues
suggested
(3).
anomeric
(5)
based
in
the
and possibly
of
is
partitioning
conA
(6) have
the presence in
in
of alcohols
the presence
of o-nitrophenyl-fl-P-galactoside 701
been
intermediate
of configuration
ratios
When the hydrolysis
glycosyl
available
of a galactosyl-enzyme
in
that
reaction.
a histidine
and transglycosidation
(1-3).
/3-galactosides
and the
catalytic
retention
D I9 75 b.v Academic Press. Inc. of reproducrim in any f&m rewnd
review the bond
(Cl)
on the
as product
that
information
involved
investigations
and a recent
carbon
little
The formation
products,
(11,
the
Relatively
residue
implicated. has been
enzyme-catalyzed
one between (4).
cerning
the
of Mw 520,000
of
Vol. 64, No. 2, 1975
(ONPG)
BIOCHEMICAL
was studied
in
enzyme-catalyzed methanol
reaction
of
to its
However,
of
with
proposed
(1,
change,
4).
intimate
suggested
(11-13)
merit
the
enzymes. is
genetic
Further, prototype This
for
our
of
two main
available
has also
a conformaintermediate
concerning
systems
relatively
little
this
likely
enzyme because
and the that
for
,9-galactosidase
reports
glycoside some of
702
vir-
effects
of
to maintain (to
-1OO'C)
mechanistic
fluid on oligoinforma-
has considerable
of the
potential
the many other
communication
which
down
intermediates First,
the
necessary
Secondly,
of using
reactions
reasons.
range
for
technique
transient
temperature
such studies
is
involving
desired
aspects it
CZ-OH,
enzyme-catalyzed
for
solvent
available in
inter-
displacement
and a covalent
accumulation
is
organic in
potential its
the
no information
solutions
tion
to slow
to allow
aqueous
a scheme
ion
a covalent
by the
in applying
to fl-galactosidase
tually the
interested
low temperatures
sufficiently
fl-galacto-
(2).
We have been very
(7).
that
involving
and a double
ion-pair,
concentra-
a carbonium
participation
from
non-enzymatic
suggested
mechanism
Recently
step
(8).
and the
has been
the
was
concentrations
(9),
intermediate
This
determining
may involve
or without
(7).
are possible
An alternative
with
has been
it
of
increasing
low methanol
methanol
lysozyme
hydrolyses
galactosyl-enzyme
tional
at high
glycosides
(10).
been
rate
rate
with
off
at
explanations
sidase-catalyzed
reaction,
in
thegalactosyl-enzyme
From analogy
mediate
levelled
a change
formation
the
increased
and then
alternative
hydrolysis
of methanol
initially
to indicate
solvolysis tion
the presence
concentration
interpreted
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
knowledge
concerning
obtaining
mutants.
could
serve
as a
hydrolases. our preliminary
findings,
BIOCHEMICAL
Vol. 64, No. 2, 1975
in
particular
mediate
which
below
-20"
Material from
direct
evidence
for
may be readily
in
50% aqueous
accumulated dimethyl
K12 by standard
dimethyl
acetate
buffer
sulfoxide (0.05
(ONPG)
was obtained
volume
of DMSO at 0' and adding
in
6-7 range.
the
these
studies
foxide with
Solutions
calcium M),
pH 7.0
and i-~ = 0.1
were made using kinetic
kinetic
were pH 7.0 determined burst
ture
(tris),
experiments
initial
temperature
was monitored experiment.
3-fold
with
An aliquot
Repeated
runs
substrate
was omitted. experiments.
within
following
manner. were cooled
550 to 415 nm. f 0.15'
during
(stock
solution
were
then
taken
in
which
either
The data
703
changes
were
The low-temperature
scans done
(12).
and Km
Vmx
and carefully
NO spectral
measurements
activity
was added
were also
buffer
previously
50% DMSO, pH 6.1 from
drying
Low temperature
the
of enzyme
wavelength
Control
control
in
in
and scanned
50% DMSO buffer)
= 0.
burst
method.
out
sul-
tris
/I-galactosidase
velocity
in
were made either
= 2 x 10e2 M.
and maintained
minutes.
these
and [S]
were carried
entire
time
25', the
Buffers
for
after
were done in
as described
conditions
M, and pH values
were used
at 37'
cold
desired
The dimethyl
118C spectrophotometer.
of ONPG (2 x 10m2M)
desired
basis.
and o-nitrophenol
were performed assay
using
Solutions the
a Cary
Sigma.
the
u = 0.1
distillation
Kinetic
experiments
Standard
KC1 to give
M (KCl).
at 0'.
from
pH with
The 0% DMSO runs
1 or 50 mM in MgC12.
and stored
of 50% and 65% (v/v)
by vacuum
hydride.
and purified
were made by mixing
appropriate
and made up on a weight
was purified
(0.05
was isolated (14)
the
at temperatures
sulfoxide.
(DMSO) solutions
M) of
inter-
and trapped
procedures
o-Nitrophenyl-fi-g-galactoside Aqueous
a galactosyl-enzyme
fi-galactosidase
and Methods. --E. coli
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Temperathe diluted
mixed for
at several
enzyme
were observed
were analyzed
to
in
by plotting
or
Vol. 64, No. 2, 1975
A440 vs.
BIOCHEMICAL
time.
The slope
of
to 'rnax, and the intercept the burst of ONP. In the were obtained were run
at
Results.
from
in
Initial
of DMSO on the
ONPG.
At pH 7.0,
to decreased enzyme per
day.
aqueous
stability
DMSO for
of
typical plot
(% DMSO)
values
All
of
for
E.
experiments
which
the
in
gives
experimental
parameters
for
the
0
4.6
l
0.5
50
5.0
* 0.5
At pH 6.1
704
in Table
hydrolyis
an energy
due
DMSO the rate
of
7%
0% and 50% I.
Figure
of ONPG
of activation
conditions
hydrolysis
0 and 50% aqueous
Km (M x 104)
linear
shown in the
cata-
apparently
at the
from
of
reduced
At 50% aqueous
are
the
hydrolysis
of Km and kcat
obtained
Under
25'
values
and O',
activity
conditions
26 f 3 kcal/mole.
Solvent
a.
the
DMSO, pH 6.1
pH 7.1,
magnitude
at determining
25'
enzyme.
losing
at 0",
Catalytic
-22".
proportional
DMSO considerably
at both
in 50% aqueous
I.
at
were aimed
of the
1 shows the Arrhenius
Table
the
,8-galactosidase-catalyzed
was observed
Comparison
is
of kcat
experiments
in 65% aqueous
was stable
= 0 yields
determination
experiments
activity
line
duplicate.
effect
lytic
the resulting
at time
burst
least
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
the
of
turnover
of ONPG,
DMSO, 50 mM MgC12.
k cat set -1 1.6
x lo3
3 . 4 x lo2
(4 . 8 x 102)
a
BIOCHEMICAL
Vol. 64, No. 2, 1975
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
I
I
I
I
33
35
37
39
+ (“K-‘1
Figure
1. Arrhenius plot for the fi-galactosidase-catal zed hydrolysis of ONPG, pH 6.1, 50% DMSO, So = 2 x lo- Y! M, 50 mM MgC12, Eo = 3.7 x 10-T M, kcat in see-l,
reaction high
becomes enzyme
o-nitrophenol
very
tions
were directly
Discussion.
initial
temperatures
At such
the
under
proportional of using
this
work. with
where
is negligible
turnover
galactosyl-enzyme of the
enzyme
substrate enzyme
subzero
concentrations,
and is
the
the bursts condi-
concentration.
is
to allow readily
of o-nitrophenol, conditions
presence
in accord
at very
bursts
saturating
under
indicates
intermediate
of
temperatures
of bursts
even
rapid
intermediate
The presence
stoichiometric
-20'
magnitude
to the
of an enzyme-substrate
in
below
temperatures
Both
rates
The utility
detection
scheme
at
were observed.
2) and the
apparent
slow
concentration.
(Fig.
the
x IO3
of a
with
a minimum
form
E+S$ES
k2,
EG
k3
705
bE+P2
(Scheme
1)
of
Vol. 64, No. 2, 1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
E, (mg/ml)
Figure
where
2. Magnitude of o-nitrophenol bursts as a function of enz e concentra3on. pH 6.1, 50% DMSO, -22", So = 2 x lo- 9 M, 50 mM MgC12. Under these experimental conditions the burst reaction was over within a few seconds and no attempts were made to measure its rate.
ES = Michaelis
Complex,
EG = galactosyl-enzyme,
o-nitrophenol
and P2 = galactose.
when turnover
is
quently
the
to that
of k3.
essentially
temperature
at
on studies
25",
than the
it
15).
accumulation
studies
will
means
dependence
of kcat
affected
reported
in
in Fig.
report
is
the
first
of a galactosyl-enzyme be directed
the
k2 is not
that
Conse-
k2 >> k3.
1 corresponds
energy
of activation
by temperature
of transglycosylation
This
that
PI = of such bursts
k2 has a much lower
much less
has been
k3 (7,
The presence
zero
Apparently
and is consequently Based
x IO
changes,
presence
of alcohols
substantially direct
greater
evidence
Subsequent
intermediate.
at elucidating
the
for
nature
of the
inter-
mediate. Since
the bursts
of o-nitrophenol
with
the
amount
of active
over
is negligible,
they
site
normality
that
the
obtained
in
this
may be used (16).
preparation study
under
enzyme,
titrations
enzyme
should
(Table
conditions
was 61% active. are
706
where
as the basis
The results
I)
be stoichiometric
in accord
in
for Fig.
active 2 indicate
The values with
turn-
of Km
reported
BIOCHEMICAL
Vol. 64, No. 2, 1975
values
of Km for
the
different
the
reaction
site
enzyme.
for
of
in
the
50% DMSO.
two-fold
water
with
decrease
based
and catalytic
I)
and presumably
reflects
active
site
on the
appear (Fig.
Acknowledgement.
This
from
Science
;:
2: 5. 6. 7.. 8. 9.
only
the
water
effect
in
50%
anticipated
concentration
was
of DMSO on the
of this
enzyme
for
kcat
obtained
than
than
previously
fact
that
crystalline
to be only
galactosyl-
appears to be due to +2 of Mg in the presence
properties
the
of 50% DMSO
were no specific
at pH 7.1
reduced
of the
is higher
normality
the National
in kcat I)
of
A 50% de-
of the
at 1 mM Mg+'
studies
of DMSO (Table
reaction.
there
and effect
The value
B-galactosidase
if
to
sensitivity
The presence
the hydrolysis
example
structural
shortly.
the
0% DMSO (Table
Detailed
of
in
pH optimum For
(1).
for
decrease
observed.
reported
I)
due no doubt
and the
ions
be expected
The five-fold
DMSO compared changes
metal
on Km (Table would
considerably,
conditions
to various
in kcat
binding
vary
experimental
has no effect crease
ONPG which
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
in
60% active
will the
be absence
reported
(7)
preparations based
on the
2).
investigation
was supported
by a grant
Foundation.
Wallenfels, K. & Weil, R. (1972) Enzymes 7, 617 Sinnott, M. L. & Souchard, I.J.L. (1973) Xiochem. J. 133, 89. Stokes, T. M. & Wilson, I. B. (1972) Biochemistry ll, 1061. Wallenfels, K. & Malhotra, 0. P. (1961) Adv. Carbo. Chem. 16, 239 Yariv, J., Wilson, K. J., Hildesheim, J. & Blumberg, S. (1971) FEBS Letts. 15, 24. Proctor, M. H. (196n, Biochem. Biophys. Acta. 59, 713. Tenu, J. P., Viratelle, 0. M., Garnier, J., & Yon, J. (1971) European J. Biochem. 20, 363. Sinnott, M. L. & Viratelle, 0. M. (1973) Biochem. J. 133 81. Imoto, T., Johnson, L.N., North, A. C. T., Philips, D.C. & Rupley, J. A. (1972), Enzymes 7, 665. Lee, Y. C. (1969), Biochem. Bio Eys. Res. Comm. 35, 161. Fink, A. L. & Good, N. E. (19747 ibid., 58, 126.-
1’1”:
707
Vol. 64, No. 2, 1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Fink, A. L. (1973), Biochemistry l2, 1736. Fink, A. L. (1975), submitted for publication. Craven, G. P., Steers, E. & Anfinsen, C. B. (1965), J. Biol. Chem. 240, 2668. Van Der Groen, G., Wouters-Leysen, J., Yde, M. & De Bruyne, C. K. D. (1973), European,J. Biochem. 38, 122. Bender, M. L. Begue-Canton,M. L., Bla&ly, R. L., Brubacher, L. J., Feder, J., Gunter, C. R., K&dy, F. J., Killheffer, Jr., J. V., Marshall, T. H., Miller, C. G., Roeske, R. W. and Stoops, J. K. (1966), J. Amer. Chem. Sot. 88 , 5890.
708
Vol. 64, No. 2, 1975
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
THE /3-GAIACTOSIDASE-CATALYZED g-GALACTOSIDE
OF c-NITROPHENOL-B-
AT SUBZERO TEMPERATURES:
GAIACTOSYL-ENZYME
EVIDENCE FOR A
INTERMEDIATE
Anthony Division
HYDROLYSIS
L. Fink
of Natural
Santa
Cruz,
California
Received
April
2,1975
and Kim J.
Sciences,
Angelides
University
of California,
95064.
The reaction of fl-galactosidase (E. coli Kl2) with oenyl-/3-D-galactoside has been inves'figax over the tmrange=-t-25O to -30' using 50% aqueous dimethyl sulfoxide as solvent. At temperatures below -10' turnover becomes very slow and a burst of o-nitrophenol is observed. Such a burst indicates the existence of a galactosyl-enzyme intermediate whose breakdown is rate-limiting and provides a means of determining the active site normality. The Arrhenius plot for turnover is linear in the -25 to +25O range with Ea = 26 f 3 kcal/mole. The presence of the 50% DMSO had no effect on Km but caused a small decrease in kcat.
==T nltrop perature
/3-Galactosidase which
has been
K12 is a tetramer
from 5.
the
subject
of several
recent
concerning its mechanism of action, From H2 18 0 and other studies it is
clear
is
cleaved
hydrolysis
is
the
oxygen
in
the
methionine
the
as well
alcohol
Copyright AII rights
residues
suggested
(3).
anomeric
(5)
based
in
the
and possibly
of
is
partitioning
conA
(6) have
the presence in
in
of alcohols
the presence
of o-nitrophenyl-fl-P-galactoside 701
been
intermediate
of configuration
ratios
When the hydrolysis
glycosyl
available
of a galactosyl-enzyme
in
that
reaction.
a histidine
and transglycosidation
(1-3).
/3-galactosides
and the
catalytic
retention
D I9 75 b.v Academic Press. Inc. of reproducrim in any f&m rewnd
review the bond
(Cl)
on the
as product
that
information
involved
investigations
and a recent
carbon
little
The formation
products,
(11,
the
Relatively
residue
implicated. has been
enzyme-catalyzed
one between (4).
cerning
the
of Mw 520,000
of
Vol. 64, No. 2, 1975
(ONPG)
BIOCHEMICAL
was studied
in
enzyme-catalyzed methanol
reaction
of
to its
However,
of
with
proposed
(1,
change,
4).
intimate
suggested
(11-13)
merit
the
enzymes. is
genetic
Further, prototype This
for
our
of
two main
available
has also
a conformaintermediate
concerning
systems
relatively
little
this
likely
enzyme because
and the that
for
,9-galactosidase
reports
glycoside some of
702
vir-
effects
of
to maintain (to
-1OO'C)
mechanistic
fluid on oligoinforma-
has considerable
of the
potential
the many other
communication
which
down
intermediates First,
the
necessary
Secondly,
of using
reactions
reasons.
range
for
technique
transient
temperature
such studies
is
involving
desired
aspects it
CZ-OH,
enzyme-catalyzed
for
solvent
available in
inter-
displacement
and a covalent
accumulation
is
organic in
potential its
the
no information
solutions
tion
to slow
to allow
aqueous
a scheme
ion
a covalent
by the
in applying
to fl-galactosidase
tually the
interested
low temperatures
sufficiently
fl-galacto-
(2).
We have been very
(7).
that
involving
and a double
ion-pair,
concentra-
a carbonium
participation
from
non-enzymatic
suggested
mechanism
Recently
step
(8).
and the
has been
the
was
concentrations
(9),
intermediate
This
determining
may involve
or without
(7).
are possible
An alternative
with
has been
it
of
increasing
low methanol
methanol
lysozyme
hydrolyses
galactosyl-enzyme
tional
at high
glycosides
(10).
been
rate
rate
with
off
at
explanations
sidase-catalyzed
reaction,
in
thegalactosyl-enzyme
From analogy
mediate
levelled
a change
formation
the
increased
and then
alternative
hydrolysis
of methanol
initially
to indicate
solvolysis tion
the presence
concentration
interpreted
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
knowledge
concerning
obtaining
mutants.
could
serve
as a
hydrolases. our preliminary
findings,
BIOCHEMICAL
Vol. 64, No. 2, 1975
in
particular
mediate
which
below
-20"
Material from
direct
evidence
for
may be readily
in
50% aqueous
accumulated dimethyl
K12 by standard
dimethyl
acetate
buffer
sulfoxide (0.05
(ONPG)
was obtained
volume
of DMSO at 0' and adding
in
6-7 range.
the
these
studies
foxide with
Solutions
calcium M),
pH 7.0
and i-~ = 0.1
were made using kinetic
kinetic
were pH 7.0 determined burst
ture
(tris),
experiments
initial
temperature
was monitored experiment.
3-fold
with
An aliquot
Repeated
runs
substrate
was omitted. experiments.
within
following
manner. were cooled
550 to 415 nm. f 0.15'
during
(stock
solution
were
then
taken
in
which
either
The data
703
changes
were
The low-temperature
scans done
(12).
and Km
Vmx
and carefully
NO spectral
measurements
activity
was added
were also
buffer
previously
50% DMSO, pH 6.1 from
drying
Low temperature
the
of enzyme
wavelength
Control
control
in
in
and scanned
50% DMSO buffer)
= 0.
burst
method.
out
sul-
tris
/I-galactosidase
velocity
in
were made either
= 2 x 10e2 M.
and maintained
minutes.
these
and [S]
were carried
entire
time
25', the
Buffers
for
after
were done in
as described
conditions
M, and pH values
were used
at 37'
cold
desired
The dimethyl
118C spectrophotometer.
of ONPG (2 x 10m2M)
desired
basis.
and o-nitrophenol
were performed assay
using
Solutions the
a Cary
Sigma.
the
u = 0.1
distillation
Kinetic
experiments
Standard
KC1 to give
M (KCl).
at 0'.
from
pH with
The 0% DMSO runs
1 or 50 mM in MgC12.
and stored
of 50% and 65% (v/v)
by vacuum
hydride.
and purified
were made by mixing
appropriate
and made up on a weight
was purified
(0.05
was isolated (14)
the
at temperatures
sulfoxide.
(DMSO) solutions
M) of
inter-
and trapped
procedures
o-Nitrophenyl-fi-g-galactoside Aqueous
a galactosyl-enzyme
fi-galactosidase
and Methods. --E. coli
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Temperathe diluted
mixed for
at several
enzyme
were observed
were analyzed
to
in
by plotting
or
Vol. 64, No. 2, 1975
A440 vs.
BIOCHEMICAL
time.
The slope
of
to 'rnax, and the intercept the burst of ONP. In the were obtained were run
at
Results.
from
in
Initial
of DMSO on the
ONPG.
At pH 7.0,
to decreased enzyme per
day.
aqueous
stability
DMSO for
of
typical plot
(% DMSO)
values
All
of
for
E.
experiments
which
the
in
gives
experimental
parameters
for
the
0
4.6
l
0.5
50
5.0
* 0.5
At pH 6.1
704
in Table
hydrolyis
an energy
due
DMSO the rate
of
7%
0% and 50% I.
Figure
of ONPG
of activation
conditions
hydrolysis
0 and 50% aqueous
Km (M x 104)
linear
shown in the
cata-
apparently
at the
from
of
reduced
At 50% aqueous
are
the
hydrolysis
of Km and kcat
obtained
Under
25'
values
and O',
activity
conditions
26 f 3 kcal/mole.
Solvent
a.
the
DMSO, pH 6.1
pH 7.1,
magnitude
at determining
25'
enzyme.
losing
at 0",
Catalytic
-22".
proportional
DMSO considerably
at both
in 50% aqueous
I.
at
were aimed
of the
1 shows the Arrhenius
Table
the
,8-galactosidase-catalyzed
was observed
Comparison
is
of kcat
experiments
in 65% aqueous
was stable
= 0 yields
determination
experiments
activity
line
duplicate.
effect
lytic
the resulting
at time
burst
least
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
the
of
turnover
of ONPG,
DMSO, 50 mM MgC12.
k cat set -1 1.6
x lo3
3 . 4 x lo2
(4 . 8 x 102)
a
BIOCHEMICAL
Vol. 64, No. 2, 1975
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
I
I
I
I
33
35
37
39
+ (“K-‘1
Figure
1. Arrhenius plot for the fi-galactosidase-catal zed hydrolysis of ONPG, pH 6.1, 50% DMSO, So = 2 x lo- Y! M, 50 mM MgC12, Eo = 3.7 x 10-T M, kcat in see-l,
reaction high
becomes enzyme
o-nitrophenol
very
tions
were directly
Discussion.
initial
temperatures
At such
the
under
proportional of using
this
work. with
where
is negligible
turnover
galactosyl-enzyme of the
enzyme
substrate enzyme
subzero
concentrations,
and is
the
the bursts condi-
concentration.
is
to allow readily
of o-nitrophenol, conditions
presence
in accord
at very
bursts
saturating
under
indicates
intermediate
of
temperatures
of bursts
even
rapid
intermediate
The presence
stoichiometric
-20'
magnitude
to the
of an enzyme-substrate
in
below
temperatures
Both
rates
The utility
detection
scheme
at
were observed.
2) and the
apparent
slow
concentration.
(Fig.
the
x IO3
of a
with
a minimum
form
E+S$ES
k2,
EG
k3
705
bE+P2
(Scheme
1)
of
Vol. 64, No. 2, 1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
E, (mg/ml)
Figure
where
2. Magnitude of o-nitrophenol bursts as a function of enz e concentra3on. pH 6.1, 50% DMSO, -22", So = 2 x lo- 9 M, 50 mM MgC12. Under these experimental conditions the burst reaction was over within a few seconds and no attempts were made to measure its rate.
ES = Michaelis
Complex,
EG = galactosyl-enzyme,
o-nitrophenol
and P2 = galactose.
when turnover
is
quently
the
to that
of k3.
essentially
temperature
at
on studies
25",
than the
it
15).
accumulation
studies
will
means
dependence
of kcat
affected
reported
in
in Fig.
report
is
the
first
of a galactosyl-enzyme be directed
the
k2 is not
that
Conse-
k2 >> k3.
1 corresponds
energy
of activation
by temperature
of transglycosylation
This
that
PI = of such bursts
k2 has a much lower
much less
has been
k3 (7,
The presence
zero
Apparently
and is consequently Based
x IO
changes,
presence
of alcohols
substantially direct
greater
evidence
Subsequent
intermediate.
at elucidating
the
for
nature
of the
inter-
mediate. Since
the bursts
of o-nitrophenol
with
the
amount
of active
over
is negligible,
they
site
normality
that
the
obtained
in
this
may be used (16).
preparation study
under
enzyme,
titrations
enzyme
should
(Table
conditions
was 61% active. are
706
where
as the basis
The results
I)
be stoichiometric
in accord
in
for Fig.
active 2 indicate
The values with
turn-
of Km
reported
BIOCHEMICAL
Vol. 64, No. 2, 1975
values
of Km for
the
different
the
reaction
site
enzyme.
for
of
in
the
50% DMSO.
two-fold
water
with
decrease
based
and catalytic
I)
and presumably
reflects
active
site
on the
appear (Fig.
Acknowledgement.
This
from
Science
;:
2: 5. 6. 7.. 8. 9.
only
the
water
effect
in
50%
anticipated
concentration
was
of DMSO on the
of this
enzyme
for
kcat
obtained
than
than
previously
fact
that
crystalline
to be only
galactosyl-
appears to be due to +2 of Mg in the presence
properties
the
of 50% DMSO
were no specific
at pH 7.1
reduced
of the
is higher
normality
the National
in kcat I)
of
A 50% de-
of the
at 1 mM Mg+'
studies
of DMSO (Table
reaction.
there
and effect
The value
B-galactosidase
if
to
sensitivity
The presence
the hydrolysis
example
structural
shortly.
the
0% DMSO (Table
Detailed
of
in
pH optimum For
(1).
for
decrease
observed.
reported
I)
due no doubt
and the
ions
be expected
The five-fold
DMSO compared changes
metal
on Km (Table would
considerably,
conditions
to various
in kcat
binding
vary
experimental
has no effect crease
ONPG which
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
in
60% active
will the
be absence
reported
(7)
preparations based
on the
2).
investigation
was supported
by a grant
Foundation.
Wallenfels, K. & Weil, R. (1972) Enzymes 7, 617 Sinnott, M. L. & Souchard, I.J.L. (1973) Xiochem. J. 133, 89. Stokes, T. M. & Wilson, I. B. (1972) Biochemistry ll, 1061. Wallenfels, K. & Malhotra, 0. P. (1961) Adv. Carbo. Chem. 16, 239 Yariv, J., Wilson, K. J., Hildesheim, J. & Blumberg, S. (1971) FEBS Letts. 15, 24. Proctor, M. H. (196n, Biochem. Biophys. Acta. 59, 713. Tenu, J. P., Viratelle, 0. M., Garnier, J., & Yon, J. (1971) European J. Biochem. 20, 363. Sinnott, M. L. & Viratelle, 0. M. (1973) Biochem. J. 133 81. Imoto, T., Johnson, L.N., North, A. C. T., Philips, D.C. & Rupley, J. A. (1972), Enzymes 7, 665. Lee, Y. C. (1969), Biochem. Bio Eys. Res. Comm. 35, 161. Fink, A. L. & Good, N. E. (19747 ibid., 58, 126.-
1’1”:
707
Vol. 64, No. 2, 1975
BIOCHEMICAL
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
Fink, A. L. (1973), Biochemistry l2, 1736. Fink, A. L. (1975), submitted for publication. Craven, G. P., Steers, E. & Anfinsen, C. B. (1965), J. Biol. Chem. 240, 2668. Van Der Groen, G., Wouters-Leysen, J., Yde, M. & De Bruyne, C. K. D. (1973), European,J. Biochem. 38, 122. Bender, M. L. Begue-Canton,M. L., Bla&ly, R. L., Brubacher, L. J., Feder, J., Gunter, C. R., K&dy, F. J., Killheffer, Jr., J. V., Marshall, T. H., Miller, C. G., Roeske, R. W. and Stoops, J. K. (1966), J. Amer. Chem. Sot. 88 , 5890.
708
