Regulation of Aspartate Aminotransferase Isozymes by d-Erythrose 4-Phosphate and Glycoladehyde Phosphate, the Naturally Occurring Homologues of d-Glyceraldehyde 3-Phosphate
As part of a study of the regulation of aspartate aminotransferase isozymes (EC 2.6.1.1), we have investigated the characteristics of inhibition of the anionic and cationic isozymes by d -erythrose 4-phosphate and glycolaldehyde phosphate, the naturally occurring homologues of d -glyceraldehyde 3-ph...
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Published in | The Journal of biological chemistry Vol. 247; no. 10; pp. 3262 - 3268 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
American Society for Biochemistry and Molecular Biology
25.05.1972
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Online Access | Get full text |
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Summary: | As part of a study of the regulation of aspartate aminotransferase isozymes (EC 2.6.1.1), we have investigated the characteristics
of inhibition of the anionic and cationic isozymes by d -erythrose 4-phosphate and glycolaldehyde phosphate, the naturally occurring homologues of d -glyceraldehyde 3-phosphate.
Erythrose-4-P has been found to be a time-dependent inhibitor of both the cationic and anionic isozymes. The inhibitor dissociation
constants and types of inhibition were determined from residual enzyme activity after equilibration of each isozyme with the
inhibitor and one substrate in the preliminary incubation mixtures. Inhibition of both isozymes by erythrose-4-P was completely
competitive with respect to α-ketoglutarate and completely noncompetitive with respect to aspartate. The K i values of the cationic isozyme were 1.44 and 0.135 m m for the pyridoxal and pyridoxamine forms, respectively. The K i values of the anionic isozyme were 3.04 and 0.33 m m for the pyridoxal and pyridoxamine forms, respectively. Both forms of the cationic isozyme were more sensitive to inhibition
than the corresponding forms of the anionic isozyme.
Inhibition of aspartate aminotransferase isozymes by glycolaldehyde-P was complete and not time-dependent. Inhibition was
competitive with respect to α-ketoglutarate as the variable substrate and uncompetitive with respect to aspartate as the variable
substrate. The K i values were 1.07 and 0.79 m m for the pyridoxamine form of the cationic and anionic isozymes, respectively.
The characteristics of the inhibition of aspartate aminotransferase isozymes by erythrose-4-P, glyceraldehyde-3-P, and glycolaldehyde-P
are not related to number of carbon atoms in these compounds.
Kinetic analyses of the binding of glycolaldehyde-P and glyceraldehyde-3-P to the isozymes showed that their binding is mutually
exclusive.
The results suggest that glyceraldehyde-3-P and its naturally occurring homologues erythrose-4-P and glycolaldehyde-P may
be involved in the regulation of gluconeogenesis in vivo by affecting the activity of the isozymes of aspartate aminotransferase. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/S0021-9258(19)45240-X |