Reciprocal enzymatic interference of carnitine palmitoyltransferase I and glycerol-3-phosphate acyltransferase in purified liver mitochondria.

(i) Highly purified mitochondrial fractions were practically devoid of microsomal contamination and of acyl-CoA ligase activity. (ii) In mitochondria, glycerol-3-phosphate acyltransferase (GPAT) activity was supported by two enzymes, the first being very active at low palmitoyl-CoA/albumin ratios and sensitive to external agents (external form), the second being detected only at higher palmitoyl-CoA/albumin ratios and insensitive to external agents (internal form). (iii) Carnitine palmitoyltransferase I (CPT I) activity was shown to inhibit external GPAT activity only. (iv) Glycerol-3-phosphate exerted an inhibitory effect on CPT I, even when GPAT was inactive. Reciprocal interaction of CPT I and GPAT was discussed with regard to the balance existing between fatty acid oxidation and esterification metabolic pathways.