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  • Title: Differential binding of NAD+ to acyl glyceraldehyde-3-phosphate dehydrogenase and its role in the acyl group transfer reaction.
    Author: Malhotra OP.
    Journal: Indian J Biochem Biophys; 1991 Aug; 28(4):257-62. PubMed ID: 1752628.
    Abstract:
    Enzyme protein fluorescence of di-furylacryloyl-glyceraldehyde-3-phosphate dehydrogenase (di-FA-GPDH:lambda max.excitation 290 nm, lambda max.emission 338 nm) is quenched about 28% on saturation with NAD+. Results of fluorometric titration of di-FA-GPDH with NAD+ suggest the presence of two tight and two loose coenzyme binding sites (Kdiss. 0.1 and 6.0 microM, respectively). Initial rates of the NAD(+)-dependent reaction of di-FA-GPDH with arsenate and phosphate and of mono-FA-GPDH with phosphate have been determined at varying coenzyme concentrations. The data suggest that binding of NAD+ at the tight sites does not activate the acyl group for its reaction with the acceptor (phosphate or arsenate). The group transfer reaction is dependent only on NAD+ binding to the loose sites, which carry the acyl group. The large difference in the NAD+ binding affinity to the two types of sites and their different effects on the group transfer reaction impart a sigmoidal shape to the rate versus [NAD+] plots. The sigmoidicity is abolished if the reactive SH groups at the unacylated sites are blocked by carboxymethylation.
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