Metabolic fate of leucine: a significant sterol precursor in adipose tissue and muscle.

ROSENTHAL, J., A. ANGEL, AND J. FARKAS. Metabolic fate of leucine: a sign$kant sterol precursor in adipose tissue and muscle. Am. J. Physiol. 226(2) : 411-418. 1974.-The quantitative significance of muscle and adipose tissue as extrahepatic sites of leucine metabolism was studied. The rate of leucine conversion to either CO* or total lipid expressed per gram wet weight of tissue was adipose tissue > muscle > liver. Insulin increased the rate of leucine conversion to total lipids and sterols in adipose tissue but not in muscle or liver. The incorporation of leucine to protein was greatest in liver, followed by adipose tissue, then muscle. In terms of total organ activity, leucine utilization (i.e., conversion to CO2 + total lipid + protein) in adipose tissue and muscle combined was 7 times greater than that of liver. Leucine conversion to nonsaponifiable lipids in adipose tissue and muscle combined exceeded that occurring in liver. The incorporation of leucine carbons into fatty acid and nonsaponifiable lipids in adipose tissue was linear over physiological concentrations of substrate (0. l-l .O mM). Both leucine and glucose served equally well in the synthesis of nonsaponifiable lipids in adipose tissue. Thus, adipose tissue and muscle are major extrahepatic sites of leucine metabolism, and leucine is a significant precursor for sterol biosynthesis in adipose tissue.