Biosynthesis of valine and isoleucine in plants II. Dihydroxyacid dehydratase from Phaseolus radiatus

• Published in: Biochimica et biophysica acta Vol. 92; no. 2; pp. 367 - 377
• Main Authors: Satyanarayana, T., Radhakrishnan, A.N.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 22.11.1964
• Subjects: Amino Acids - metabolism; Chemical Phenomena; Chemistry; Chloromercuribenzoates; Chromatography; Enzyme Inhibitors; Ethylmaleimide; Hydro-Lyases; Iron; Isoleucine; Kinetics; Magnesium; Manganese; Mercury; OldMedline; Phaseolus; Plants; Silver; Sulfhydryl Compounds; Valine; PHMB; DHIV; KIV; KMV; DHMV; ETHYLMALEIMIDE; ENZYME INHIBITORS; EXPERIMENTAL LAB STUDY; SILVER; VALINE; IRON; SULFHYDRYL COMPOUNDS; CHROMATOGRAPHY; MAGNESIUM; MERCURY; MANGANESE; KINETICS; ISOLEUCINE; CHEMISTRY; PLANTS; CHLOROMERCURIBENZOATES; HYDRO-LYASES; AMINO ACID METABOLISM
• ISSN: 0926-6569; 0006-3002; 1878-2248
• DOI: 10.1016/0926-6569(64)90195-6

1. 1. An enzyme catalysing the conversion of α,β-dihydroxyisovalerate and α,β-dihydroxy-β-methylvalerate to α-ketoisovalerate and α-keto-β-methylvalerate has been partially purified from green gram ( Phaseolus radiatus), and its characteristics studied. 2. 2. A natural inhibitor, heat stable and inorganic in nature, was observed in the crude extracts. 3. 3. The observed K m values for α-β-dihydroxyisovalerate and α,β-dihydroxy-β-methylvalerate were 2.4 · 10 −3 M and 9 · 10 −4 M, respectively. 4. 4. The enzyme required the presence of a divalent metal ion (Mg 2+, Mn 2+ or Fe 2+) for maximal activity. Heavy metals like Ag + and Hg 2+ were inhibitory. 5. 5. The optimal activity was around pH 8.0 and the optimum temperature at 52°. The activation energy is found to be 12 600 cal/mole. 6. 6. The enzyme was inhibited by p-hydroxymercuribenzoate, N-ethylmaleimide and sulphydryl compounds like cysteine, glutathione, 2-mercaptoethanol and 2,3-dimercaptopropanol. The inhibition by p-hydroxymercuribenzoate could not be reversed by any of the sulfhydryl compounds tested.