Transamination and Oxidative Decarboxylation Rates of Branched-Chain 2-Oxo Acids in Cultured Human Skin Fibroblasts

Abstract

ABSTRACT. Transamination and oxidative decarboxylation of branched-chain L-amino acid derived 2-oxo acids in cultured human skin fibroblasts from normal subjects and from a patient with maple syrup urine disease (variant form) were comparatively studied in incubations with 1-¹⁴C-labeled substrates (1 mmol/liter). With normal cells, ¹⁴CO₂ release ranged from about 11 to 3 nmol/90 min/mg of cell protein in the order 3-methyl-2-oxo[¹⁴C]butanoate > (S)-3-methyl-2-oxo[¹⁴C]pentanoate > 4-methyl-2-oxo[¹⁴C]pentanoate > (R)-3-methyl-2-oxo[¹⁴C]pentanoate. Formation of the corresponding branched-chain amino[¹⁴C] acids was substantially higher than ¹⁴CO₂ production (around 10-fold) and similar with L-valine, L-isoleucine, and L-leucine. L-Allo-isoleucine production [from (R)-3-methyl-2-oxopentanoate] was significantly lower. With maple syrup urine disease fibroblasts, comparable transamination rates were observed. Related to the findings with normal cells, ¹⁴CO₂ release from each substrate was differently reduced and apparent residual branched-chain 2-oxo acid dehydrogenase complex activity with 3-methyl-2-oxobutanoate, 4-methyl-2-oxopentanoate, (S)-, and (R)-3-methyl-2-oxopentanoate amounted to 12, 13, 22, and 50%, respectively.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD