DIFFERENTIAL PHOSPHOLIPID-LABELING SUGGESTS 2 SUBTYPES OF PHOSPHOLIPASE-D IN RAT LEYDIG-CELLS

The aim of the present study was to compare the transphosphatidylation activity of phospholipase D (PLD) under different substrate labeling conditions, in order to investigate whether PLD in rat Leydig cells ex hibited any substrate preferences for the alkyl- or acyl-form of phosp hatidylcholine (PtdCho). The [H-3]phosphatidylethanol formation in res ponse to 4B-phorbol 12-myristate 13-acetate (PMA), sphingosine, or Ca+-ionophore A23187, was lower when Leydig cells were labeled with 1-O- [H-3]alkyl lysoPtdCho compared with the responses when [H-3]myristic a cid was employed. In contrast, the results for the receptor agonists ( vasopressin, bradykinin, and lysophosphatidic acid), using the two lab els, showed more consistency. Thus, the PLD-activity induced by PMA, s phingosine, or A23187 has a more selective substrate range (i.e. mainl y acyl-linked PtdCho) than the PLD-activity stimulated via a receptor. Our data suggests the existence of PLD isozymes that differ with resp ect to substrate specificity and activation mechanisms. (C) 1995 Acade mic Press, Inc.