Kinetics of product inhibition and mechanisms of XXXX activation by apolipoprotein C-II.

@entity844 @entity41837 @entity3952 @entity571 @entity291 @entity18050
The kinetics of product inhibition of @entity291 milk @entity41837 ( @entity41837 ) were studied in a system of emulsified @entity18050 (TG) at different fixed initial concentrations of @entity3952 [( @entity571 ]0) without a @entity844 (FA) acceptor. In the absence of apolipoprotein C-II (C-II), the apparent Vmax and the nH(TG) (the slope of the corresponding Hill plot for TG) of 1.82 decreased by about 52% and [TG]0.5 increased 13-fold by raising the [ @entity571 ]0 to 0.3 mM. At low [ @entity571 ]0, product inhibition was competitive with respect to TG: the nH( @entity571 ) averaged 1.1, and [ @entity571 ]0.5 was increased about 2-fold by TG. At the higher [ @entity571 ]0, nH( @entity571 ) was 3.5, and TG had no effect on [ @entity571 ]0.5. In the presence of 3 micrograms/mL C-II, the apparent Vmax was 4.3-7.1-fold higher than in its absence, and the nH(TG) was 2.45. Both parameters decreased by only 20-25%, and [TG]0.5 increased only 3-fold at an [ @entity571 ]0 of 0.3 mM. Conversely, nH( @entity571 ) decreased by 35% and [ @entity571 ]0.5 increased 6-fold by increasing TG concentrations. Similar kinetics were observed with very low density lipoproteins (VLDL). At saturating TG and varying C-II concentrations, nH(C-II) was 1.78, and product inhibition was found to be competitive with respect to C-II. At the [ @entity571 ]0 employed, the FA had no effect on enzyme binding to TG emulsions, and there was no evidence that @entity41837 catalyzes the reverse reaction. It is concluded that (a) the @entity41837 kinetics are those of a multisite enzyme that probably has three high-affinity binding sites for TG, two for C-II, and four for @entity571 .(ABSTRACT TRUNCATED AT 250 WORDS)
