Study on development of drugs for endocrine and metabolic disorders based on properties of new enzyme

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Acetoacetyl-CoA (AA-CoA) synthetase is a novel ligase, which specifically activates acetoacetate to AA-CoA. This enzyme is mainly involved in lipid and cholesterol biosynthesis in the liver, and the physiological role of AA-CoA synthetase is not clear yet. This let us to develop new drugs by the elucidation of new enzyme. First, cloning of the enzyme cDNA was carried out being based on the amino acid sequence determined from the enzyme preparation purified from rat liver. Consequently, both the obtained rat and human AA-CoA synthetase genes consisted of 2016 nucleotides, and coded 672 amino acid residues. Homology of amino acid sequence between rat and human was 89.3%. Expression of this enzyme was high in brain, and its expression profile was similar to that of HMG-CoA reductase, the rate-limiting enzyme of cholesterol biosynthesis. In human brain, expression of the enzyme was high in cerebral cortex, especially in hippocampus, which is located inner side part of temporal lobe, and expression profile of the AA-CoA synthetase was similar to that of HMG-CoA reductase. In diabetic rats injected with streptozotocin (STZ), hepatic AA-CoA synthetase activity started to gradually decrease similarly as HMG-CoA reductase and reached one tenth of the initial activity. When rats were fed with the diet supplemented with hypocholesterolemic agents, pravastatin and cholestyramine, the degree of STZ-induced decrease in AA-CoA synthetase activity was diminished, and ketone body concentration in blood was decreased to the normal level. These results indicate that hepatic AA-CoA synthetase may partly contribute to the regulation of blood ketone body, and that this enzyme expressed highly in hippocampus of human brain may have the important role in memory function.