Effects of CoA and acyl-CoAs on GTP-dependent Ca2+ release and vesicle fusion in rat liver microsomal vesicles.
(1) CoA (IC50 23 microM) and acyl-CoAs (IC50 values 15-18 microM) inhibit GTP-dependent vesicle fusion in rat liver microsomal vesicles. Acyl-CoAs of carbon chain length C8 and C20 are much less effective than acyl-CoAs of carbon chain length C14-C18. The effect of CoA is mimicked by dephospho-CoA, but not by desulpho-CoA. High acyl-CoA concentrations (50 microM) appear to favour formation of small vesicles (budding), while 50 microM CoA does not. (2) Low concentrations of CoA (EC50 2 microM) and palmitoyl-CoA (10 microM) cause re-accumulation of Ca2+ released in response to GTP. This re-accumulation is into an Ins(1,4,5)P3-sensitive compartment. By investigation of the effects of CoA and palmitoyl-CoA on the thapsigargin-induced passive leak rate of Ca2+, and on the latency of the mannose-6-phosphatase of the vesicles, we conclude that CoA and palmitoyl-CoA cause decreased vesicle permeability rather than stimulation of Ca2+ pumping activity. (3) It is suggested that GTP-induced membrane fusion in rat liver microsomes involves an as yet uncharacterized acylation-deacylation reaction which is required to produce complete vesicle sealing.
School of Biological Sciences, University of East Anglia, Norwich, U.K.
J G
JG
Comerford
A P
AP
Dawson
D000214:Acyl Coenzyme A / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D003065:Coenzyme A / Q000494:pharmacology*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008561:Membrane Fusion / Q000187:drug effects*; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D010171:Palmitoyl Coenzyme A / Q000494:pharmacology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D051381:Rats; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D000214:Acyl Coenzyme A; D013729:Terpenes; D010171:Palmitoyl Coenzyme A; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; C023553:mannose-6-phosphatase; D010744:Phosphoric Monoester Hydrolases; D020558:GTP Phosphohydrolases; D000252:Calcium-Transporting ATPases; D003065:Coenzyme A; D002118:Calcium