title: Vitamin K-dependent carboxylase: effect of ammonium sulfate on substrate carboxylation and on inhibition by stereospecific substrate analogs.
abstract: (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.
authors.affiliation: Department of Biochemistry, University of Limburg, Maastricht, The Netherlands.
authors.forename: B A
authors.initials: BA
authors.lastname: Soute
authors.forename: F
authors.initials: F
authors.lastname: Acher
authors.forename: R
authors.initials: R
authors.lastname: Azerad
authors.forename: C
authors.initials: C
authors.lastname: Vermeer
mesh_terms: 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
chemical_list: D009842:Oligopeptides; D011498:Protein Precursors; D008025:Ligases; D019735:Carbon-Carbon Ligases; C020660:glutamyl carboxylase; D000645:Ammonium Sulfate