A novel Ca2+-dependent phospholipase D from Streptomyces tendae, possessing only hydrolytic activity

Abstract

An extracellular phospholipase D (PLD(St)) was purified from Streptomyces tendae by two successive chromatographic steps on Sepharose CL-6B and DEAE-Sepharose CL-6B. Molecular weight of the PLD(St) was estimated to be approximately 43 kDa by sodium dodecyl sulfatepolyacrylamide gel electrophoresis. Maximal activity was at pH 8 and 60 degrees C, and the enzyme was stable at or below 60 degrees C and between pH 8 and 10, when assayed after 1.5 and 24 h, respectively. The enzyme activity had an absolute requirement of Ca(2+), and the maximum activity was at 2 mM CaCl(2). The Km and Vmax values for phosphatidyl choline were 0.95 mM and 810 micromol min(-1) mg(-1), respectively. More importantly, PLD(St) could not catalyze transphosphatidylation of glycerol, L-serine, myo-inositol and ethanolamine, which have been extensively used to evaluate the activity. The result strongly suggests that PLD( St ) does not have the transphosphatidylation activity, thereby making it the first Streptomyces PLD possessing only hydrolytic activity. PLD(St) may therefore be a novel type of PLD enzyme.