Altered release of carnitine palmitoyltransferase activity by digitonin from liver mitochondria of rats in different physiological states

Abstract

The release of carnitine palmitoyltransferase (CPT) activity from rat liver mitochondria by increasing concentrations of digitonin was studied for mitochondrial preparations from fed, 48 h-starved and diabetic animals. A bimodal release of activity was observed only for mitochondria isolated from starved and, to a lesser degree, from diabetic rats, and it appeared to result primarily from the enhanced release of approx. 40% and 60%, respectively, of the total CPT activity. This change in the pattern of release was specific to CPT among the marker enzymes studied. For all three types of mitochondria there was no substantial release of CPT concurrently with that of the marker enzyme for the soluble intermembrane space, adenylate kinase. These results illustrate that the bimodal pattern of release of CPT reported previously for mitochondria from starved rats [Bergstrom & Reitz (1980) Arch. Biochem. Biophys. 204, 71-79] is not an immutable consequence of the localization of CPT activity on either side of the mitochondrial inner membrane. Sequential loss of CPT I (i.e. the overt form) from the mitochondrial inner membrane did not affect the concentration of malonyl-CoA required to effect fractional inhibition of the CPT I that remained associated with the mitochondria. The results are discussed in relation to the possibility that altered enzyme-membrane interactions may account for some of the altered regulatory properties of CPT I in liver mitochondria of animals in different physiological states.

Malonyl-CoA binding site and the overt carnitine palmitoyltransferase activity reside on the opposite sides of the outer mitochondrial membrane.

“…CPT with increase in [digitonin] has been found to follow a bimodal curve with mitochondria of fasted but not with those of fed rats (32). Moreover, the CPT solubilization profile has paralleled near-concurrent solubilization of an OM marker, monoamine oxidase, in one study (32), of an intermembrane marker, adenylate kinase, in another (26), and of a matrix marker, citrate synthase, in the third (9).…”

“…Moreover, the CPT solubilization profile has paralleled near-concurrent solubilization of an OM marker, monoamine oxidase, in one study (32), of an intermembrane marker, adenylate kinase, in another (26), and of a matrix marker, citrate synthase, in the third (9).…”

Role of insulin in hepatic fatty acid partitioning: emerging concepts

“…The activity of CPT I to convert acyl-CoA into acylcarnitine, and the reversal of this reaction by CPT II in the inner-membranematrix compartment (connected by the transport of the acylcarnitine by a specific carrier located in the inner membrane), results in the effective transfer of long-chain fatty-acyl molecules across the inner membrane while leaving the acyl-CoA pools in the cytosolic and matrix compartments separate. CPT I resides in the outer membrane of the mitochondria [34] and is an integral membrane protein [35,36], whereas CPT II is a peripheral protein of the inner membrane, with its active site facing the matrix space. CPT I is the one that is sensitive to malonyl-CoA.…”

Hormonal and nutritional control of liver fatty acid oxidation and ketogenesis during development

“…The hormonal regulation of the sensitivity of CPT I to malonyl-CoA inhibition could include: (1) an alteration in the conformation of CPT I within the outer mitochondrial membrane [38], (2) a modification in the fluidity of the outer mitochondrial membrane [39], (3) a modification in the microenvironment of CPT I [40], and (4) an association with the microsomal membranes [ 4 11.…”