SIGNIFICANT CONTRIBUTION OF ARGININE-112 AND ITS POSITIVE CHARGE OF PSEUDOMONAS-PUTIDA CYTOCHROME P-450(CAM) IN THE ELECTRON-TRANSPORT FROMPUTIDAREDOXIN
K. Nakamura et al., SIGNIFICANT CONTRIBUTION OF ARGININE-112 AND ITS POSITIVE CHARGE OF PSEUDOMONAS-PUTIDA CYTOCHROME P-450(CAM) IN THE ELECTRON-TRANSPORT FROMPUTIDAREDOXIN, Biochimica et biophysica acta. Protein structure and molecular enzymology, 1207(1), 1994, pp. 40-48
Cytochrome P-450(cam) of Pseudomonas putida is a prototype of various
eukaryotic cytochrome P-450 molecules. Arg-112 located on the surface
of this protein is highly conserved among various other cytochromes P-
450. In this study, we constructed mutant genes for P-450(cam) in whic
h Arg-112 was replaced by Gln or Glu, expressed them in Escherichia co
li and purified the mutant proteins. Their P-450 enzymic activities we
re analyzed in the reconstituted system to determine the function of A
rg-112. K-d values for d-camphor of Arg(112)-Gln and Arg(112)-Glu were
much the same as those of the wild-type enzyme, whereas K-d values fo
r the oxidized form of putidaredoxin, which is an acidic protein and i
s the redox partner of P-450(cam) were 240 and 530 mu M, respectively.
These values are 8 and 19 times larger than that of the wild-type enz
yme (28 mu M), thereby indicating lower affinities of the mutant enzym
es for the oxidized putidaredoxin. Reaction rate constants for reducti
on by the reduced form of putidaredoxin, measured using the stopped fl
ow method, were 45.5, 9.0.10(-3) and 9.0.10(-4) s(-1) for the wild typ
e, Arg(112)-Gln and Arg(112)-Glu, respectively. Thus, Arg-112 of P-450
(cam) plays an important role in the interaction with putidaredoxin an
d in the high efficiency of the electron transfer; the positive charge
of the residue seeming to contribute to the process. The yields in Es
cherichia coli, the heme contents in the purified fractions and heat s
tability of the mutant proteins were lower than those of the wild type
enzyme, suggesting that Arg-112 of P-450(cam) is also important for s
tability of P-450(cam).