The sidedness of carnitine acetyltransferase and carnitine octanoyltransferase of rat liver endoplasmic reticulum.

The location of carnitine acetyltransferase and carnitine octanoyltransferase on the inner and outer surfaces of rat liver microsomes was investigated. Latency of mannose-6-phosphate phosphate showed that the microsomes were 90-94% sealed. All of the octanoyltransferase is associated with the cytosolic face, while the acetyltransferase is distributed between the cytosolic face (68-73%) and the lumen face (27-32%) of the endoplasmic reticulum membrane. Small amounts of trypsin inhibit the carnitine octanoyltransferase equally in either sealed or permeable microsomes but the acetyltransferase of sealed microsomes is stimulated. Large amounts of trypsin inhibit all transferase activities by about 60%, expect for acetyltransferase of sealed microsomes. Other studies show that 0.1% Triton X-100 partially inhibits carnitine octanoyltransferase of microsomes but does not inhibit the acetyltransferase or any of the mitochondrial carnitine acyltransferase.