Date of Award

Fall 1984

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry & Biochemistry

Program/Concentration

Chemistry

Committee Director

James H. Yuan

Committee Member

John D. Van Norman

Committee Member

Kenneth G. Brown

Call Number for Print

Special Collections LD4331.C45W43

Abstract

Glycerol-3-phosphate dehydrogenase catalyzes the reversible reaction:

NAD+ + G-3-P ⇌ NADH + DHAP + H+

The enzyme is found in organisms from E. coli to man. The primary function of the enzyme varies from organism to organism. Depending on the metabolism of the organism, the enzyme may function primarily to generate G-3-P for lipid (in organisms with a highly aerobic biosynthesis metabolism), or it may function primarily to produce NAD+ to support glycolysis. Complex multicellular organisms possess tissue specific isozymes of GPDH whose kinetic parameters reflect the relative importance of G-3-P and NAD+ production in various tissues.

In eukaryotic organisms, the enzyme exists in two forms within a Dinucleotide-dependent single form cell: a Flavin Adenine imbedded within the inner mitochondrial membrane, and a soluble cytosolic form which is NAD+ dependent. The two forms participate in the "Glycerol-3-phosphate shuttle'' which acts to shuttle the reducing glycolysis, equivalents produced in the cytosol during into the mitochondrion. The operation of the shuttle is most prominent in tissues such as skeletal muscle which glycolyze heavily. In such tissues, a cytosolic [NAD+] [/NADH] ratio of 500 must be maintained despite the rapid production of NADH by glycolysis. Since the rate of glycolysis may vary widely in skeletal muscle, a mechanism must exist to adjust the reactivity of the cytosolic GPDH to transient changes in metabolite concentration. A negatively cooperative NAD binding effect would provide that control.

Experiments by Rosevear (I) revealed a negatively cooperative binding effect in the case of both rabbit and chicken muscle GPDH with 3-aminopyridine adenine dinucleotide, a competitive inhibitor of NAD+, using the technique of fluorescence quenching. Since the confirmation of this result by an independent method would be of extreme interest in light of the foregoing discussion, an equilibrium binding analysis was made of GPDH from both chicken muscle and rabbit muscle. The negative cooperativity observed by Rosevear was confirmed for enzymes from both sources. The further observation by Rosevear that this cooperativity was abolished by the addition of saturating amounts of G-3-P was also confirmed. Binding constants derived in this study agreed with those derived by Rosevear but values for subunit number differed from accepted values for these two enzymes.

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DOI

10.25777/7vpz-0088

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