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Resolution and Brain Regional Distribution of Cysteine Sulfinate Decarboxylase Isoenzymes from Hog Brain
Author(s) -
Spears Ronald M.,
Martin David L.
Publication year - 1982
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.1471-4159.1982.tb05339.x
Subject(s) - glutamate decarboxylase , glutamate receptor , chemistry , cysteine , biochemistry , specific activity , isozyme , enzyme , receptor
Abstract: Cysteine sulfinate decarboxylase (CSD; EC 4.1.1.29) activity from porcine brain was resolved into three peaks by hydroxylapatite chromatography. The first two peaks (I and II) did not decarboxylate and were not inhibited by glutamate. The third peak (III) cochromatographed with glutamate decarboxylase (GAD; EC 4.1.1.15) activity. The K m values of cysteine sulfinate for peaks I, II, and III were 5.5 × 10 −4 m , 1.3 × 10 −4 m , and 4.5 × 10 −3 m , respectively. The possibility that the same enzyme was responsible for peak III CSD and GAD activities was suggested by several findings: (1) Mutual competitive inhibition was observed between glutamate and cysteine sulfinate for these activities. (2) Similar first‐order heat‐inactivation curves were obtained for peak III CSD and GAD when incubated at 55xBOC. (3) Both activities were inhibited similarily by ATP and chloride ion. High concentrations of glutamate (0. l m ) inhibited peak III CSD activity more than 90% but had no effect on either peak I or II CSD activities. This difference in sensitivity of the isoenzymes to inhibition by glutamate was used to examine the relative regional distributions and the relative contributions to total activity of the glutamate‐sensitive (peak III CSD, GAD) and glutamate‐insensitive (peaks I and II CSD) isoenzymes. Glutamate‐insensitive CSD activity contributed only part of the total activity in all brain regions tested (ranging from 23% in the superior colliculus to 64% in the pons). However, the specific activity of glutamate‐insensitive CSD was more constant than the total or glutamate‐sensitive specific activities among the brain regions tested. The results indicate that GAD is responsible for a significant proportion of the total CSD activity in porcine brain.