Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Biochemistry, Biophysics and Molecular Biology

Abstract

To determine the chemical mechanism of the reaction catalyzed by adenylosuccinate synthetase, positional isotope exchange studies were performed. Positional isotope exchange from the (beta)-(gamma) bridge to the (beta) nonbridge position of (gamma)-('18)O GTP was followed using ('31)P NMR. The positional isotope exchange was found to occur in the presence of either IMP or IMP and succinate. The exchange did not occur in the presence of asparate. These results support a reaction mechanism which involves formation of a 6-phosphoryl-IMP intermediate with subsequent attack by aspartate to form adenylosuccinate as originally proposed by Lieberman in 1956 Lieberman, I. J. Biol. Chem., 1956, 223, 327-339 ;In order to resolve the NMR resonances for positional isotope exchange, it was necessary to find a chelator which would limit exchange broadening. trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic acid was found to be a suitable chelator at neutral and acidic pH;Studies of adenylosuccinate synthetase from Escherichia coli have been limited by the low concentrations of enzyme present in the cell and the difficulty in purifying the enzyme to homogeneity. Overproduction of the enzyme by cloning the purA gene into a runaway replication plasmid allowed the cells to produce a much higher concentration of enzyme. A new purification scheme is reported that takes advantage of the overproduced enzyme. Yields of 75 mg of homogeneous enzyme have been obtained from 76 g of E. coli cell paste.

DOI

https://doi.org/10.31274/rtd-180813-10925

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Michael Brian Bass

Language

en

Proquest ID

AAI8716742

File Format

application/pdf

File Size

96 pages

Included in

Biochemistry Commons

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