Characterization of overt carnitine palmitoyltransferase in rat platelets; involvement of insulin on its regulation.
Saponin-permeabilization (30 micrograms/ml) of the platelet plasma membrane, which enables access of added compounds to mitochondrial overt carnitine palmitoyltransferase (CPT I), was applied to allow the rapid determination of CPT I activity in situ. The effects of diabetes and short-term incubation with insulin in vitro on the kinetic parameters and malonyl-CoA sensitivity of CPT I were also studied in rat platelets. CPT I exhibited ordinary Michaelis-Menten kinetics when platelets were incubated with palmitoyl-CoA. Malonyl-CoA showed an I50 (concentration giving 50% inhibition of CPT activity) of 0.92 +/- 0.11 microM in permeabilized platelets. Platelets obtained from diabetic rats (induced by streptozotocin injection) exhibited an increased Vmax and I50 for malonyl-CoA, and an unaltered Km for palmitoyl-CoA. In contrast, preincubation of platelets prepared from both fed control rats and diabetic rats with insulin (100 and 150 microU/ml) led to a decrease in enzyme activity when assayed with 75 microM palmitoyl-CoA and 0.5 mM L-carnitine as substrates. These in vivo and in vitro results suggested that insulin directly modulated rat platelet CPT I activity, as it does in the liver.
Iida
R
R
Department of First Internal Medicine, Kansai Medical University, Osaka, Japan.
Takeyama
N
N
Iida
N
N
Tanaka
T
T
D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D002334:Carnitine O-Palmitoyltransferase / Q000097:blood*; D002463:Cell Membrane Permeability; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000201:enzymology*; D005969:Glutamate Dehydrogenase / Q000097:blood; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D007527:Isoenzymes / Q000097:blood*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000097:blood; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012503:Saponins
D007328:Insulin; D007527:Isoenzymes; D012503:Saponins; D007770:L-Lactate Dehydrogenase; D005969:Glutamate Dehydrogenase; D002334:Carnitine O-Palmitoyltransferase