Our research is concerned with the early steps in the metabolism of inorganic sulfur and nitrogen compounds. Major emphasis is on ATP sulfurylase and APS kinase from the filamentous fungus Penicillium chrysogenum. The fungal ATP sulfurylase has been purified to homogeneity and partially characterized kinetically, physically, and chemically. Our current efforts are aimed at (a) elucidating the mechanism of the reaction, (b) identifying the amino acid residues responsible for the functional integrity of the enzyme, and (c) exploring the potential interaction of ATP sulfurylase with APS kinase. Parallel studies are in progress on the ATP sulfurylase from Penicillium duponti (a thermophile). Our work with the P. duponti enzyme may shed some light on the factors responsible for the remarkable heat stability of this enzyme. APS kinase, the second sulfate activating enzyme has been purified to homogeneity from P. chrysogenum and is being characterized. Studies on the sulfate reduction pathway of fungi will be initiated. Other proposed projects include studies on nitrate reductase and nitrite reductase from P. chrysogenum, with particular emphasis on the kinetic mechanisms of these enzymes. Some of the methods that will be employed include (a) analysis of steady-state and reaction progress kinetics, (b) equilibrium ligand binding with native and chemically modified enzymes, and (c) chemical modification of specific amino acid residues.

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National Institute of General Medical Sciences (NIGMS)
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Microbial Physiology and Genetics Subcommittee 2 (MBC)
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University of California Davis
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Martin, R L; Daley, L A; Lovric, Z et al. (1989) The ""regulatory"" sulfhydryl group of Penicillium chrysogenum ATP sulfurylase. Cooperative ligand binding after SH modification;chemical and thermodynamic properties. J Biol Chem 264:11768-75
Yu, M; Martin, R L; Jain, S et al. (1989) Rat liver ATP-sulfurylase: purification, kinetic characterization, and interaction with arsenate, selenate, phosphate, and other inorganic oxyanions. Arch Biochem Biophys 269:156-74
Segel, I H; Martin, R L (1988) The general modifier (""allosteric"") unireactant enzyme mechanism: redundant conditions for reduction of the steady state velocity equation to one that is first degree in substrate and effector. J Theor Biol 135:445-53
Renosto, F; Martin, R L; Segel, I H (1987) ATP sulfurylase from Penicillium chrysogenum. Molecular basis of the sigmoidal velocity curves induced by sulfhydryl group modification. J Biol Chem 262:16279-88
Daley, L A; Renosto, F; Segel, I H (1986) ATP sulfurylase-dependent assays for inorganic pyrophosphate: applications to determining the equilibrium constant and reverse direction kinetics of the pyrophosphatase reaction, magnesium binding to orthophosphate, and unknown concentrations of pyrophosp Anal Biochem 157:385-95
Renosto, F; Seubert, P A; Knudson, P et al. (1985) Adenosine 5'-phosphosulfate kinase from Penicillium chrysogenum. Determining ligand dissociation constants of binary and ternary complexes from the kinetics of enzyme inactivation. J Biol Chem 260:11903-13
Hunter, D R; Segel, I H (1985) Evidence for two distinct intracellular pools of inorganic sulfate in Penicillium notatum. J Bacteriol 162:881-7
Seubert, P A; Renosto, F; Knudson, P et al. (1985) Adenosinetriphosphate sulfurylase from Penicillium chrysogenum: steady-state kinetics of the forward and reverse reactions, alternative substrate kinetics, and equilibrium binding studies. Arch Biochem Biophys 240:509-23
Chen, L J; Segel, I H (1985) Purification and characterization of bile salt sulfotransferase from human liver. Arch Biochem Biophys 241:371-9
Renosto, F; Seubert, P A; Knudson, P et al. (1985) APS kinase from Penicillium chrysogenum. Dissociation and reassociation of subunits as the basis of the reversible heat inactivation. J Biol Chem 260:1535-44

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