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Characterization of overt carnitine palmitoyltransferase in rat platelets; involvement of insulin on its regulation

Summary

Saponin-permeabilization (30 µg/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 µM 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 µ-cU/ml) led to a decrease in enzyme activity when assayed with 75 µM 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.

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Correspondence to Reimi Iida.

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Iida, R., Takeyama, N., Iida, N. et al. Characterization of overt carnitine palmitoyltransferase in rat platelets; involvement of insulin on its regulation. Mol Cell Biochem 103, 23–30 (1991). https://doi.org/10.1007/BF00229590

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Key words

  • diabetes
  • malonyl-CoA inhibition
  • rat platelets
  • insulin
  • carnitine palmitoyltransferase
  • saponin