Some Properties of Long Fatty Acyl-Coenzyme A Thioesterase in Rat Organs

Abstract

Long fatty acyl-Coenzyme A thioesterase [EC 3.1.2.2] is widely distributed in mammalian tissues. The enzyme activity (per g wet weight of tissue) in rats was found to be 8 to 10 times higher in brain and testis than in liver, kidney, heart or blood cells (erythrocytes). The enzyme was purified 40 to 60 fold from these tissues and the substrate specificities of preparations from the various tissues were compared using C₆-, to C₁₈-acyl-Coenzyme A thioesters. The enzyme hydrolyzed C₈ to C₁₈ thioesters, C₁₄ and C₁₆ thioesters being the best substrates, with K_m values 3 to 5×10⁻⁶ M. Preparations from the various tissues had similar substrate specificities. Moreover the molecular weights of enzymes from these tissues were all estimated to be about 50,000, by sucrose density gradient centrifugation. However, the gel filtration patterns of the enzymes from different tissues were not similar and the patterns were classified into three types: 1) liver type, 2) heart; kidney, and spleen type, and 3) brain, testis and blood cell type. The enzyme activity was detected in blood plasma in rats intoxicated with CCl₄ and the gel filtration pattern showed that this enzyme was released into the blood plasma only from the cytoplasm of the liver.