Abstract
Hydrolysis activity of phospholipase D from Streptomyces chromofuscus (PLD) was studied in small unilamellar vesicles (SUV) of egg yolk phosphatidylcholine (PC). The enzyme was associated with PC-SUV in a Ca 2+-dependent manner. Both apparent maximum velocity, V max,(app), and reciprocal of apparent Michaelis constant, i.e., apparent binding constant, 1 K m (app), increased with Ca 2+ concentration, and the maximum values of these kinetic parameters were obtained at about 20 μM Ca 2+. Incorporation of 1,2-diacyl-glycerol (DAG), cholesterol (Chol) or α-tocopherol (Toc) into PC-SUV induced shift of the antisymmetric PO 2 − stretching band of PC to lower frequency. The neutral lipids in SUV brought about increase of the V max(app) value (Yamamoto et al. (1993) Biochim. Biophys. Acta 1145, 293–297). On the basis of these findings we discussed the regulation of PLD activity in terms of the Ca formation of PLD with SUV, and the enhancement of susceptibility of the P-O bond in PC molecule by neutral lipids.
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