Kinetics of human and bovine milk lipoprotein lipase and the mechanism of enzyme activation by apolipoprotein C-II.
The kinetics of human and bovine milk lipoprotein lipase (HM-LPL and BM-LPL, respectively) were compared by varying apolipoprotein C-II (C-II) or triacylglycerol (TG) concentrations. The apparent Km (TG) and Km (C-II) for HM-LPL were 2.2 and 6.7-fold higher than for BM-LPL. Plots of 1/v vs 1/[TG] or 1/[C-II] intercepted the respective abscissas at the same points: C-II had no effect on Km (TG) and TG had no effect on Km (C-II). Replots of slope 1/s vs 1/[C-II] gave straight lines which yielded KA values identical to Km (C-II). It is concluded that the HM-LPL system follows a random, bireactant, rapid equilibrium mechanism as shown previously for BM-LPL.