Vitamin K-dependent carboxylase: effect of ammonium sulfate on substrate carboxylation and on inhibition by stereospecific substrate analogs.
(1) High concentrations of ammonium sulfate may stimulate the carboxylase activity of bovine liver microsomes about 10-fold. This effect results from an increase of the Vmax, whereas neither the apparent Km for a number of substrates nor the Ki for substrate analogs is affected. (2) The effect of ammonium sulfate was only found in substrates lacking the pro-sequence. No effect was measurable on the carboxylation of pro-PT28 and endogenous precursor proteins. (3) If the pro-fragment was added as a peptide not covalently bound to a carboxylatable substrate, the carboxylation thereof was only slightly affected and ammonium sulfate remained active as a stimulator of carboxylase activity. (4) S-MeTPT is a much stronger inhibitor of carboxylase activity than is R-MeTPT. (5) The inhibition of carboxylase by the methylated tripeptides is competitive and independent of the type of substrate. Also pro-PT28, which contains the full pro-sequence, could be inhibited completely. (6) On the other hand the carboxylation of endogenous protein precursors could only be partly inhibited by the substrate analogs: even at high concentrations of S-MeTPT a residual endogenous substrate carboxylation of about 30% was left.
Soute
B A
BA
Department of Biochemistry, University of Limburg, Maastricht, The Netherlands.
Acher
F
F
Azerad
R
R
Vermeer
C
C
D000645:Ammonium Sulfate / Q000494:pharmacology*; D019735:Carbon-Carbon Ligases; D007700:Kinetics; D008025:Ligases / Q000032:analysis* / Q000037:antagonists & inhibitors; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology; D011498:Protein Precursors / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity
D009842:Oligopeptides; D011498:Protein Precursors; D008025:Ligases; D019735:Carbon-Carbon Ligases; C020660:glutamyl carboxylase; D000645:Ammonium Sulfate