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Metabolisme du γ‐aminobutyrate chez Agaricus bisporus III. La succinate‐semialdehyde:NAD(P) + oxydoreductase
Author(s) -
BALDY PIERRETTE
Publication year - 1977
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1977.tb01501.x
Subject(s) - nad+ kinase , oxidoreductase , glycerol 3 phosphate dehydrogenase , chemistry , dehydrogenase , thiamine pyrophosphate , enzyme , biochemistry , cofactor , stereochemistry
Metabolism of γ‐Aminobutyrate in Agaricus bisporus. III. The Succinate‐Semialdehyde: NAD (P) + Oxidoreductase. The succinate‐semialdehyde:NAD(P) + oxidoreductase (E.C. 1.2.1.16) is responsible for the second step in the catabolism of γ‐aminobutyrate: the irreversible enzymatic conversion of succinic semialdehyde (SSA) to succinate. Succinate semialdehyde dehydrogenase was extracted from mitochondrial fraction of fruit‐bodies of Agaricus bisporus Lge. The mitochondrial pellet was sonicated and centrifuged at 110,000 g; the supernatant obtained was designated the “crude extract”. The enzyme was extremely unstable on storage, unless 1 m M EDTA and 20% glycerol were added. Kinetic studies were carried out at 30°C, and the formation of NADH or NADPH was followed by measuring increase of absorbance at 340 nm with a spectrophotometer. The dehydrogenase was completely inactive when the reaction was run in the absence of thiol and was more active with NAD + than with NADP + . In the “crude extract” the activity with NADP + had a pH optimum between 8.6 and 9.1 and the K m values for SSA and NADP + were 2.0 × 10 −4 M and 1.4 × 10 −4 M respectively. The pH optimum with NAD + was found between 8.6 and 8.8 and the K m value for SSA is 4.8 × 10 −4 M and for NAD + 2.0 × 10 −3 M . With NAD + , the kinetic values (pH, K m ) of the “crude extract” chromatographed on hydroxylapatite were unchanged. Inhibition by thiamine pyrophosphate (TPP) was uncompetitive with respect to NAD + , those by malate, ATP, ADP and NADPH non‐competitive and that by NADH competitive. These results and the fact that activity with NAD + was lost more slowly than with NADP + indicate the possibility of at least two mitochondrial succinate‐semialdehyde dehydrogenases, even though the activities of this enzyme assayed with NAD + and NADP + respectively were not able to be separated from each other by hydroxylapatite column chromatography. Some speculations on the metabolic regulation of this dehydrogenase and considerations on the significance of these results in the physiology of respiration in Agaricus bisporus Lge are given.