Acta Physiologica 43. (1973)
3. szám - PHYSIOLOGIA - Kerner J.-Sándor A.-Alkonyi I.: Physiological Variations in Carnitine Acetyl-Transferase Activity in Rat Tissues: Activity in Animals Exposed to Fasting and Cold
Acta Physiologica Academiae Scientiarum Hungaricae, Tomus 43 (3), pp. 227—231 (1973) PHYSIOLOGICAL VARIATIONS IN CARNITINE ACETYL-TRANSFERASE ACTIVITY IN RAT TISSUES: ACTIVITY IN ANIMALS EXPOSED TO FASTING AND COLD By J. Kerner, A. Sándor and I. Aliconyi INSTITUTE OF BIOCHEMISTRY, UNIVERSITY MEDICAL SCHOOL, PÉCS (Received September 14, 1972) Carnitine acetyl-transferase (CAT) activity showed no diurnal variations in skeletal muscle, interscapular brown adipose tissue or the liver. Forty-eight hours of fasting had no influence on CAT activity in interscapular brown fat, the liver and the kidneys. An increase in activity was observed in the interscapular brown fat and the liver of animals kept at a low temperature for 4 weeks; in skeletal muscle the increase was not significant. The dependence of CAT activity upon the period of the cold effect has been studied in the brown adipose tissue. The following reaction is reversibly catalyzed by the enzyme carnitine acetyl-transferase (acetyl-CoA, carnitine O-acetyl-transferase, E.C. 2.3.1.7.; Friedman and Fraenkel 1955) acetyl-carnitine -(- CoASH acetyl-coA -f- (—) carnitine In addition to acetyl-CoA, CAT also reacts at a lower reaction velocity with short chain carboxylic acids among which there are branched chain and unsaturated carboxylic acids (Fritz et al. 1963; Solberg and Bremer 1970; Alkonyi and Sándor 1972). CAT plays an important role in the synthesis and degradation of fatty acids, since in the form of macroergic acetyl-carnitine it enables the transport of acetic acid through the membrane of the mitochondria (Bressler and Brendel 1966) and between the various compartments within the mitochondria (Hsu and Fritz 1967). It further represents a storage of acetyl and acyl groups in their macroergic forms in conditions associated with an increased carbohydrate and fat degradation (Childress et al. 1967; Böhmer et al. 1966; Böhmer 1967; Böhmer and Bremer 1968). Böhmer (1967) observed a significant shift in the ratio of carnitine to its various acyl derivatives in conditions associated with enhanced fat combustion (fasting, diabetes, fat feeding). This ratio shows a diurnal variation. The unsolved question whether a change in enzyme activity was necessary for an enhanced conversion of substrates has prompted us to measure CAT activity under the conditions mentioned above. Our attention was directed to brown fat, since in this adipose tissue cold exposure causes a marked increase in lipid degradation (Cameron and Smith 1964; Hull and Segal 1965) and, in comparison to other tissues Acta Physiologica Academiae Scientiarum Hungaricae 43, 1973 3