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Métabolisme du γ‐Aminobutyrate chez Agaricus bisporus
Author(s) -
BALDY PIERRETTE
Publication year - 1975
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.1399-3054.1975.tb03854.x
Subject(s) - enzyme , agaricus bisporus , fractionation , chemistry , biochemistry , glutamate decarboxylase , glyoxylate cycle , malonate , glutamate receptor , chromatography , mushroom , receptor , food science
γ‐Aminobutyrate synthesis, the first step in this pathway, is catalysed by L‐glutamate‐1‐carboxy‐lyase (E.G. 4.1.1.15). The purification procedure and some of in vitro properties of this enzyme isolated from fruit‐bodies of Agaricus bisporus 19 Lge were investigated. Glutamate decarboxylase has been partially purified from a homogenate by a combination of ammonium sulfate fractionation and hydroxylapatite column chromatography. All kinetic studies were carried out manometrically in a nitrogen atmosphere at 35°C by conventional Warburg technique. The decarboxylase is a pyridoxal‐phosphate requiring enzyme. The pH optimum was found to be between 5.5 and 5.6 and the Km value for glutamate was calculated to be 4 × 10 ‐2 M from a Lineweaver‐Burk plot. Of the amino acids tested the enzyme is specific for glutamate. γ‐Aminobutyrate is not carboxylated to form glutamate. Inhibition by malate, malonate, α‐ketoglutarate and NAD were found to be non‐competitive with respect to glutamate, and those by succinate to be uncompetitive. Fractionation of the subcellular components shows that the enzyme is localized in the hyaloplasm. The results are discussed in relation to the γ‐aminobutyrate bypath, a probable shunt to the Krebs cycle.