A kinetic investigation of fumarase reaction at high substrate concentrations

A study of the steady-state kinetics of fumarase over an extended concentration range, using novel methods of analysis, reveals an initial-rate equation of at least fourth degree for malate as substrate at pH 7.0, with no kinetically significant dead-end complex formation even up to concentrations of 100 mM. In the absence of demonstrable enzyme-aggregation phenomena, this is interpreted as indicating co-operative effects overlooked previously, although a mixture of isoenzymes, each individually of high degree and giving a complex curve, may be a contributing factor.

Section: Fig 2(b)supporting

confidence: 81%

mentioning

confidence: 99%

Deviation from Michaelis-Menten kinetics for fumarase

Crabbe¹

1976

“…Various conclusions concerning the binding of substrate to the active centre were based on these findings. Alberty et al (1954) reported substrate inhibition with malate concentrations from 33 to 100mM, as did Rajender & McCalloch (1967). These findings supported the idea of a two-point attachment of the substrate to the enzyme.…”

supporting

confidence: 59%

Lack of deviation from Michaelis–Menten kinetics for pig heart fumarase

Andersen¹

1980

Studies of steady-state kinetics of fumarase in the usual substrate-concentration range from 0.1 Km to 10 Km and in the high substrate-concentration range from 10 Km to 200 Km are described. The purpose is to investigate reports of substrate inhibition and oscillatory kinetics. In the normal substrate-concentration range, no deviations from hyperbolic kinetics were found, and in the extended concentration range, up to more than 200 times the Km value, no substrate inhibition was demonstrated. A discussion of the discrepancies between the mentioned reports of deviations from the hyperbolic kinetics and the present findings is given.

The effect of restricted hydration on the rate of reaction of glucose 6-phosphate dehydrogenase, phosphoglucose isomerase, hexokinase and fumarase. Relevance for metabolism in xeric (near-dry) conditions

Stevens

1979

A method is described for the measurement of enzyme activity under xeric conditions. The reaction mixtures had water contents ranging between 0.1 and 0.6g/g of reaction mixture. For glucose 6-phosphate dehydrogenase, hexokinase and fumarase, enzyme activity became detectable (about 0.05% of the fully hydrated rate) when the water content was about 0.2g/g of reaction mixture, and for phosphoglucose isomerase, around 0.15g/g of reaction mixture. With the water content raised to 0.3g/g of reaction mixture the reaction rates were only increased to 0.1-3% of the fully hydrated rate. When the combined rates for phosphoglucose isomerase and glucose 6-phosphate dehydrogenase were measured, reasonable agreement was found between the experimental data and those calculated from the individual experimentally determined rates on the assumption that diffusion was not further limiting. A method was devised for measuring the diffusion coefficients of low-molecular-weight substances in solutions having low water contents. The diffusion coefficients of riboflavin in sorbitol solution decreased by about 100-fold when the water content of the latter was reduced from 3 to 0.25g/g of sorbitol. It is concluded that to detect enzyme activity a certain minimal amount of water is required and that above this minimum the rate is still restricted by diffusion limitation. The relevance of the results to the physical state of water in reaction mixtures and to metabolism in seeds and spores in xeric conditions is discussed.