title: Analysis of branched-chain alpha-keto acid dehydrogenase complex activity in rat tissues using alpha-keto[1-13C]isocaproate as substrate.
abstract: We have developed a highly sensitive nonradioisotope method for the measurement of branched-chain alpha-keto acid dehydrogenase complex (BCKDC) activity using alpha-keto[1-(13)C]isocaproate ([1-(13)C]KIC) as substrate. The enzyme reaction was performed in a 10-ml test tube. After incubation of the reaction mixture (1 ml), the reaction was terminated by acidification, followed by the addition of internal standard (3.5 micromol K(2)CO(3)) for calculation of (13)CO(2). The (13)CO(2) released to the gas phase in the test tube was calculated from the molar ratio of (13)CO(2)/(12)CO(2) assayed by gas chromatography isotope ratio mass spectrometry. A distinct linear relationship between (13)CO(2) production rate and BCKDC activity was obtained when using purified BCKDC. The detection limit of (13)CO(2) in the assay method was at least 0.167 nmol, which is similar to that in the previously reported radiochemical method. The enzyme assay was found to be linear with respect to reaction time and quantity of enzyme used up to approximately 60 nmol (13)CO(2) produced. We measured BCKDC activities in several rat tissues, including skeletal muscle. The activities of BCKDC obtained are comparable to those reported previously. These results suggest that the novel BCKDC assay method using [1-(13)C]KIC is useful for measurement in tissues with low BCKDC activity such as skeletal muscle.
authors.affiliation: Department of Amino Acid Basic and Applied Research Group, Institute of Life Sciences, Ajinomoto Company, Kawasaki-ku, Kawasaki 210-8681, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Keiichi
authors.initials: K
authors.lastname: Akita
authors.forename: Ryosei
authors.initials: R
authors.lastname: Sakai
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Shimomura
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes; D002417:Cattle; D002849:Chromatography, Gas / Q000379:methods*; D057075:Enzyme Assays; D007421:Intestine, Small / Q000201:enzymology; D007651:Keto Acids / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013154:Spleen / Q000201:enzymology
chemical_list: D002247:Carbon Isotopes; D007651:Keto Acids; D002245:Carbon Dioxide; C013082:alpha-ketoisocaproic acid; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)