Target size analysis by radiation inactivation of carnitine palmitoyltransferase activity and malonyl-CoA binding in outer membranes from rat liver mitochondria

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Abstract
The functional molecular sizes of the protein(s) mediating the carnitine palmitoyltransferase I (CPT I) activity and the [14C]malonyl-CoA binding in purified outer-membrane preparations from rat liver mitochondria were determined by radiation-inactivation analysis. In all preparations tested the dose-dependent decay in [14C]malonyl-CoA binding was less steep than that for CPT I activity, suggesting that the protein involved in malonyl-CoA binding may be smaller than that catalysing the CPT I activity. The respective sizes computed from simultaneous analysis for molecular-size standards exposed under identical conditions were 60 000 and 83 000 Da for malonyl-CoA binding and CPT I activity respectively. In irradiated membranes the sensitivity of CPT activity to malonyl-CoA inhibition was increased, as judged by malonyl-CoA inhibition curves for the activity in control and in irradiated membranes that had received 20Mrad radiation and in which CPT activity had decayed by 60%. Possible correlations between these data and other recent observations on the CPT system are discussed.

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