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Apparent Inhibition of ATP Citrate Lyase by l ‐Glutamate In Vitro Is Due to the Presence of Glutamine Synthetase
Author(s) -
Rider C. C.
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb00645.x
Subject(s) - atp citrate lyase , biochemistry , glutamine synthetase , glutamate dehydrogenase , glutamine , enzyme , citrate synthase , glutamate receptor , lyase , biosynthesis , biology , glutamate synthase , amino acid , receptor
Preincubation in assay mixture for 30 min at 37°C of ATP citrate lyase from rat brain and liver results in 65–70% inhibition in the presence of 10 m M l ‐glutamate. This inhibition is specific since none of the known brain metabolites of glutamate shows this effect. ATP and ammonium sulphate‐suspended, commercially purified malate dehydrogenase are both important in the generation of inhibition; citrate and NADH are not. The ATP citrate lyase activity in desalted crude extracts and 11% polyethylene glycol‐precipitated fractions is inhibited but the enzyme purified by dye affinity chromatography is unaffected. Such purification reveals the presence of a factor responsible for the generation of the inhibition shown to be of M r 380,000. These lines of evidence implicate endogenous glutamine synthetase, and the involvement of this enzyme is established by the use of its inhibitor l ‐methionine sulphoximine and by the addition of purified glutamine synthetase to restore the glutamate inhibition of purified ATP citrate lyase. The phenomenon probably arises from the production by glutamine synthetase of ADP, a known product inhibitor of ATP citrate lyase. Therefore contrary to previous reports elswhere, l ‐glutamate has no role in the regulation of brain ATP citrate lyase and thus the supply of cytoplasmic acetyl groups for biosynthesis.