Acetone butanol ethanol (ABE) production from concentrated substrate: reduction in substrate inhibition by fed-batch technique and product inhibition by gas stripping

Studies on initial velocity and product inhibition were carried out on crystalline cytoplasmic NAD+-linked L-α-glycerophosphate dehydrogenase from rabbit muscle, at pH 7.8 and 9.0 at 26 °C. Michaelis and inhibition constants for all the reactants were determined. The kinetic data were consistent with an ordered mechanism in which nicotinamide–adenine dinucleotide (NAD+) or its reduced form (NADH) is bound to the enzyme before the addition of the glycerophosphate (LαGP) or dihydroxyacetone phosphate (DHAP) respectively. At high concentrations NADH, DHAP, and LαGP, but not NAD+, produced substrate inhibition. Combined product-inhibition and dead-end inhibition studies indicated the formation of inactive dead-end complexes of NADH–enzyme, DHAP–enzyme, and LαGP–enzyme–NADH. The low rate constant calculated for the dissociation of the active NADH–enzyme complex suggested an ordered mechanism involving either the formation of an inactive dead-end NADH–enzyme complex or an isomerized NADH–enzyme complex. A choice between these possibilities could not be made on the basis of the present kinetic data. A mechanism for substrate inhibition involving two NAD+-binding sites per mole of enzyme is proposed. Alterations of the ultraviolet absorption spectrum of the enzyme by NAD+ and NADH were in agreement with the conclusion from the kinetic results that the coenzymes are bound to the enzyme before the substrates. DHAP and LαGP caused no alteration in the enzyme spectrum. Spectral changes compatible with the formation of ternary and dead-end complexes were also detected.

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Purification and kinetic properties of ox brain histamine N-methyltransferase

Biochemical Journal ◽

10.1042/bj2330669 ◽

1986 ◽

Vol 233 (3) ◽

pp. 669-676 ◽

Cited By ~ 8

Author(s):

W L Gitomer ◽

K F Tipton

Keyword(s):

Acetic Acid ◽

Steady State ◽

Mouse Brain ◽

Initial Rate ◽

Substrate Inhibition ◽

Gel Filtration ◽

Product Inhibition ◽

Kinetic Properties ◽

Brain Histamine ◽

Inhibition Studies

Histamine N-methyltransferase (EC 2.1.1.8) was purified 1100-fold from ox brain. The native enzyme has an Mr of 34800 +/- 2400 as measured by gel filtration on Sephadex G-100. The enzyme is highly specific for histamine. It does not methylate noradrenaline, adrenaline, DL-3,4-dihydroxymandelic acid, 3,4-dihydroxyphenylacetic acid, 3-hydroxytyramine or imidazole-4-acetic acid. Unlike the enzyme from rat and mouse brain, ox brain histamine N-methyltransferase did not exhibit substrate inhibition by histamine. Initial rate and product inhibition studies were consistent with an ordered steady-state mechanism with S-adenosylmethionine being the first substrate to bind to the enzyme and N-methylhistamine being the first product to dissociate.

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Optimal substrate feeding policy for a fed batch fermentation with substrate and product inhibition kinetics

Biotechnology and Bioengineering ◽

10.1002/bit.260280916 ◽

1986 ◽

Vol 28 (9) ◽

pp. 1421-1431 ◽

Cited By ~ 99

Author(s):

J. Hong

Keyword(s):

Batch Fermentation ◽

Product Inhibition ◽

Inhibition Kinetics ◽

Fed Batch ◽

Fed Batch Fermentation ◽

Substrate Feeding

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S-Adenosylhomocysteine Metabolism in Various Species

Canadian Journal of Biochemistry ◽

10.1139/o75-044 ◽

1975 ◽

Vol 53 (3) ◽

pp. 312-319 ◽

Cited By ~ 106

Author(s):

R. D. Walker ◽

J. A. Duerre

Keyword(s):

Rat Liver ◽

Condensation Reaction ◽

Substrate Inhibition ◽

Product Inhibition ◽

Kinetic Properties ◽

Adenosylhomocysteine Hydrolase ◽

In Vivo Experiments ◽

Cleavage Enzyme

Eleven microorganisms, four plants, and major organs from the chicken, dog, rat, and rabbit were assayed for the presence of S-adenosylhomocysteine hydrolase, S-adenosyl-homocysteine nucleosidase, and S-ribosylhomocysteine-cleavage enzyme. All bacteria (procaryotes) were found to possess S-adenosylhomocysteine nucleosidase and S-ribosylhomocysteine-cleavage enzyme but not S-adenosylhomocysteine hydrolase. All eucaryotes tested, including yeasts, plants, birds, and mammals, possessed S-adenosylhomocysteine hydrolase but not S-adenosylhomocysteine nucleosidase or S-ribosylhomocysteine-cleavage enzyme. Of all the organs assayed in the vertebrates, the level of S-adenosylhomocysteine hydrolase was highest in liver, pancreas, and kidney, lower in spleen and testis, and very low in brain and heart. In all systems tested, equilibrium of the hydrolase reaction always favored synthesis over hydrolysis. We studied some of the kinetic properties of the hydrolase from rat liver. In the direction of synthesis, the Km value was 1.5 mM for adenosine and 4.5 mM for L-homocysteine, whereas marked substrate inhibition was observed with L-homocysteine. The condensation reaction is subject to product inhibition, and was inhibited by adenine. Results from in-vivo experiments revealed that the cells of the various organs of the dog are impermeable to the exogenously administered S-adenosylhomocysteine.

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