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Peroxisomal Degradation of 2‐Oxoisocaproate. Evidence for Free Acid Intermediates
Author(s) -
Gerbling Heidrun
Publication year - 1993
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1993.tb00764.x
Subject(s) - peroxisome , biochemistry , oxidative decarboxylation , oxidase test , dehydrogenase , transamination , enzyme , pipecolic acid , nad+ kinase , chemistry , decarboxylation , biology , amino acid , receptor , catalysis
Peroxisomes from mung bean hypocotyl ( Vigna radiata L.) degrade 2‐oxoisocaproate, the transamination product of leucine, via isobutyryl‐CoA and propionyl‐CoA to acetyl‐CoA. The methyl group at the C‐3 position forms a barrier to β‐oxidation. This barrier is overcome in the peroxisomes by several enzymatic steps. Senecioate (3‐methylcrotonate), 2‐hydroxyisovalerate, and 2‐oxoisovalerate were detected as free acid intermediates. Senecioate, formed from 3‐methylcrotonyl‐CoA, is transformed by enzymatic hydrolysis to 2‐hydroxyisovalerate. 2‐Hydroxyisovalerate is then oxidized to 2‐oxoisovalerate in an H 2 O 2 ‐producing reaction, exhibiting 1:1 stoichiometry of the products, by a 2‐hydroxyacid oxidase which is different from the peroxisomal marker enzyme glycollate oxidase. 2‐oxoisovalerate is activated by an NAD‐dependent oxidative decarboxylation to isobutyryl‐CoA. Accumulation of 2‐oxoisovalerate in the presence of arsenite, an inhibitor of oxidative decarboxylations, is a feature of this latter pathway of degradation of isovaleryl‐CoA or senecioate. It is concluded that the barrier caused by the methyl group of 2‐oxoisocaproate is surmounted in higher plant peroxisomes in a manner different to that in mammalian mitochondria.