O-Acetyl-L-serine sulfhydrylase-A (OASS-A) forms acetate and L-cysteine from O-acetyl-L-serine (OAS) and sulfide. One molecule of the cofactor pyridoxal 5'- phosphate (PLP) is bound in each holoenzyme protomer.

The studies described in this dissertation examine the effects of F-2,6-P2 and AMP or phosphorylation on the kinetic mechanism of d-PFK. The effect of varied pH on the activation by F-2,6-P2 is also described.

ADP-ribose polymer metabolism has been studied in human cells derived from a patient with Glutamyl Ribose Phosphate Storage Disease (GRPSD) and in mouse C3H1OT1/2 cells following oxidative stress induced by hydrogen peroxide (H202 ). It has been postulated that GRPSD resulted from an abnormality in ADP-ribose polymer metabolism. This study has shown that these cells exhibit reduced poly(ADP ribose) polymerase activity which is proposed to result from modification of the enzyme with ribose phosphate groups. The modification in the polymerase is proposed to be secondary to a defect in either ADP-ribosyl proteinlyase or an overproduction of a cellular phosphodiesterase. The metabolism of ADP-ribose polymers was rapidly altered by H202 and there were independent effects on adenine nucleotide pools. The results suggest that ADP-ribose polymer metabolism is involved in cellular defenses to oxidative stress.

A complete initial velocity study of the 6-phosphogluconate dehydrogenase from Candida utilis in both reaction directions suggests a rapid equilibrium random kinetic mechanism with dead-end E:NADP:(ribulose 5-phosphate) and E:NADPH:(6- phosphogluconate) complexes. Initial velocity studies obtained as a function of pH and using NAD as the dinucleotide substrate for the reaction suggest that the 2'-phosphate is critical for productive binding of the dinucleotide substrate. Primary deuterium isotope effects using 3-<i-6-phosphogluconate were obtained for the 6-phosphogluconate dehydrogenase reaction using NADP and various alternative inucleotide substrates.