Characterization of overt carnitine palmitoyltransferase in rat platelets; involvement of insulin on its regulation
✍ Scribed by Reimi Iida; Naoshi Takeyama; Naohiro Iida; Takaya Tanaka
- Book ID
- 104673656
- Publisher
- Springer
- Year
- 1991
- Tongue
- English
- Weight
- 596 KB
- Volume
- 103
- Category
- Article
- ISSN
- 0300-8177
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✦ Synopsis
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.