CHARACTERIZATION OF A PLASMA MEMBRANE-ASSOCIATED PRENYLCYSTEINE-DIRECTED ALPHA-CARBOXYL METHYLTRANSFERASE IN HUMAN NEUTROPHILS

Signal transduction in human neutrophils requires prenylcysteine-direc ted carboxyl methylation of ras-related low molecular weight GTP-bindi ng proteins. We now report the subcellular localization and characteri zation of a neutrophil prenylcysteine alpha carboxyl methyltransferase . The highest carboxyl methyltransferase activity copurified with biot inylated neutrophil surface membranes, supporting a plasma membrane lo calization of the enzyme. Neutrophil nuclear fractions contained littl e or no methyltransferase activity. Methyltransferase activity was det ergent-sensitive but could be reconstituted by removal of detergent in the presence of phosphatidyl choline and an anionic phospholipid. N-A cetyl-S-trans,trans-farnesyl-L-cysteine (AFC) and N-acetyl-S-all-trans -geranylgeranyl-L-cysteine (AGGC) were effective substrates for neutro phil prenylcysteine-directed methyltransferase; V(max) values for AFC and AGGC (16.4 and 22.1 pmol of methylated/mg protein/min, respectivel y) are among the highest yet reported. Although both GTPgammaS and the chemoattractant fMet-Leu-Phe stimulated methylation of ras-related pr oteins, neither affected methylation of AFC. These data suggest that n eutrophil plasma membranes contain a phospholipid-dependent, prenylcys teine-directed carboxyl methyltransferase of relatively high specific activity that modifies ras-related protein substrates in the GTP-bound , activated state.