Regulation of valine and. alpha. -ketoisocaproate metabolism in rat kidney mitochondria

Journal Article · Sat Oct 01 00:00:00 EDT 1988 · American Journal of Physiology; (USA)

OSTI ID:6289881

Miller, R H; Harper, A E ^[1]

---

1. Univ. of Wisconsin, Madison (USA)

Activities of branched-chain amino acid (BCAA) aminotransferase (BCAT) and {alpha}-keto acid dehydrogenase (BCKD) were assayed in mitochondria isolated from kidneys of rats. Rates of transamination of valine and oxidation of keto acids {alpha}-ketoisocaproate (KIC) or {alpha}-ketoisovalerate (KIV) were estimated using radioactive tracers of the appropriate substrate from amounts of {sup 14}C-labeled products formed. Because of the high mitochondrial BCAT activity, an amino acceptor for BCAT, {alpha}-ketoglutarate ({alpha}-KG) or KIC, was added to the assay medium when valine was the substrate. Rates of valine transamination and subsequent oxidation of the KIV formed were determined with 0.5 mM {alpha}-KG as the amino acceptor; these rates were 5- to 50-fold those without added {alpha}-KG. Rates of CO{sub 2} evolution from valine also increased when KIC was present; however, with KIC concentrations above 0.2 mM, rates of CO{sub 2} evolution from valine declined although rates of transamination continued to rise. When 0.05 mM KIC was added to the assay medium, oxidation of KIC was suppressed by inclusion of valine or glutamate in the medium. When valine was present KIC was not oxidized preferentially, presumably because it was also serving as an amino acceptor for BCAT. These results indicate that as the supply of amino acceptor, {alpha}-KG or KIC, is increased in mitochondria not only is the rate of valine transamination stimulated but also the rate of oxidation of the KIV formed from valine. Thus the rate of oxidation of BCAA can be controlled by factors that influence the rate and direction of BCAA transamination and, thereby, the supply of substrate for BCKD.

• OSTI ID: 6289881
• Journal Information: American Journal of Physiology; (USA), Vol. 255:4; ISSN 0002-9513
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
KETO ACIDS
METABOLISM
MITOCHONDRIA
BIOCHEMICAL REACTION KINETICS
VALINE
AMINO ACIDS
AMINOTRANSFERASES
CARBON 14 COMPOUNDS
HEMIACETAL DEHYDROGENASES
LEUCINE
OXIDATION
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHEMICAL REACTIONS
ENZYMES
KINETICS
LABELLED COMPOUNDS
NITROGEN TRANSFERASES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANOIDS
OXIDOREDUCTASES
REACTION KINETICS
TRANSFERASES
551001* - Physiological Systems- Tracer Techniques