Synthetic lipopeptides activate nucleoside diphosphate kinase in HL-60 membranes

We have put forward the hypothesis that lipopeptides (LPs) activate GTP hydrolysis by Gi-proteins in HL-60 membranes via activation of nucleoside diphosphate kinase (NDPK) as does mastoparan (MP). Therefore, we compared the effects of LPs and MP on NDPK- and GTPase activation in HL-60 membranes. In native membranes, LPs effectively activated GTP hydrolysis and moderately activated GTP formation. In solubilized membranes, the effect of LPs on GTP formation was enhanced whereas the one on GTP hydrolysis was abolished. The NDPK substrate GDP enhanced the relative stimulatory effect of LPs and MP on GTP hydrolysis in HL-60 membranes in the absence of a NTP-regenerating system. A NTP-regenerating system abrogated the potentiating effect of GDP on MP-action, whereas the effect on LP-stimulated GTP-hydrolysis was enhanced. Our data show that LPs activate NDPK in HL-60 membranes and that this activation may account for their G-protein-stimulatory activity. Membrane solubilization may impair the transfer of GTP from NDPK to Gi-protein alpha-subunits and subsequent GTP hydrolysis, whereas GTP formation remains intact, augmenting the effect of LPs on the kinase. Finally, LP- and MP-induced NDPK activation may involve different pools of GDP.