Enzymes of l-(+)-3-hydroxybutyrate metabolism in the rat

The three enzymes required for the production and utilization of l-(+)-3-hydroxybutyrate were sought in various tissues of the rat. All tissues examined contained substantial amounts of (No. 1) l-(+)-3-hydroxybutyryl CoA dehydrogenase (EC 1.1.1.35). The specific activity of (No. 2) l-(+)-3-hydroxybutyryl CoA deacylase (EC 3.1.2) was highest in liver (3.8 mU/mg in mitochondrial matrix (1 U = 1 μmol/min). Brain, heart, and skeletal muscle contained < 20% of this activity. The chromatography of liver mitochondrial “matrix” preparations on DEAE-cellulose resolved the deacylase into two peaks. Peak I hydrolyzed 2- or 3- carbon acylCoA esters more efficiently than l-(+)-3-hydroxybutyrate CoA, while Peak II activity was highest using l-(+)-3-hydroxybutyryl CoA. The K_m(app) for Peak II deacylase with l-(+)-3-hydroxybutyryl CoA was 19 μm. Acyl CoA synthetase (EC 6.2.1.2) (No. 3) was assayed with sorbate (sorboyl CoA ligase) or l-(+)-3-hydroxybutyrate (l-(+)-3-hydroxybutyryl CoA ligase). The highest specific activity for l-(+)-3-hydroxybutyryl CoA ligase was associated with brain mitochondria (8.3 mU/mg). In the “matrix” fraction of rat liver mitochondria the activities of these two acyl CoA synthetases were distinguished chromatographically and by their stability at various pH values. Heart and skeletal muscle mitochondria contained <10% of the liver activities of both ligases. These data implicate the liver as a site of l-(+)-3-hydroxybutyrate production.