An Overview on Leucine Metabolites Alpha-Ketoisocaproate (KIC) and Beta-Hydroxi-Beta-Methyl Butyrate (HMB) in Skeletal Muscle Function and Sports Performance (original) (raw)

Abstract

Alpha-ketoisocaproate (KIC) and Beta hydroxy- beta methylbutyrate (HMB) are metabolites of the amino acid leucine. The first step in HMB metabolism is the reversible transamination of leucine to KIC, which occurs mainly extrahepatically. Following this enzymatic reaction, KIC is converted to HMB by two routes: through the cytosolic enzyme KIC dioxygenase; or through formation of isovaleryl-CoA by branched-chain ketoacid dehydrogenase (BCKD) in liver, which after some steps results in HMB formation. Under normal conditions the majority of KIC is converted into isovaleryl-CoA, with approximately 5% of leucine consumed metabolized into HMB. HMB and KIC have been proposed to enhance physical performance and muscle hypertrophy via their effects on muscle proteolysis and protein synthesis. Studies investigating the mechanisms by which HMB promotes increases in strength and muscle hypertrophy are still in preliminary stages. Based on the results of these studies, it is postulated that enha...

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