ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
The effects of adenine nucleotides and glutamate on glutamate decarboxylase were studied in a dialyzed, high-speed supernatant of rat brain. When incubated with 10 μm-pyridoxal-P the enzyme was strongly inhibited by ATP, ADP and their Mg2+ complexes at concentrations which were well below tissue levels. The enzyme was not significantly inhibited by 15 mm-AMP or by 100 μM-3′-5’cyclic AMP or 3′-5’cyclic GMP. Inhibition by the nucleotides cannot be described in conventional steady-state kinetic terms. Addition of ATP in the presence of pyridoxal-P resulted in a slow, progressive decrease in the reaction rate which was similar to the inactivation observed when the enzyme was incubated in the absence of pyridoxal-P. The progressive inactivation in the presence of ATP was minimal at concentrations of glutamate which were well below Km and became much more pronounced at higher glutamate concentrations. Addition of suprasaturating amounts of pyridoxal-P late in the incubation when the enzyme was almost completely inactivated resulted in an immediate and complete reactivation of the enzyme. Inhibition by ATP could be prevented by addition of saturating amounts of pyridoxal-P at the start of the reaction and was also relieved by addition of potassium phosphate buffer. The results suggest that inhibition by the nucleotides involves the prior formation of the inactive apoenzyme which results from the glutamate-promoted dissociation of pyridoxal-P. In the absence of the nucleotides, the enzyme is normally reactivated by the added pyridoxal-P. The nucleotides act to block this reassociation of pyridoxal-P with the apoenzyme thereby producing a progressive inactivation of the enzyme. The implications of these results for the regulation of GABA synthesis are discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1978.tb06539.x
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