Deviations from Michaelis-Menten kinetics. The possibility of complicated curves for simple kinetic schemes and the computer fitting of experimental data for acetylcholinesterase, acid phosphatase, adenosine deaminase, arylsulphatase, benzylamine oxidase, chymotrypsin, fumarase, galactose dehydrogenase, β-galactosidase, lactate dehydrogenase, peroxidase and xanthine oxidase

Abstract

The possible graph shapes for one-site/two-state and substrate-modifier models are discussed. The two-state model is a version of the Monod-Wyman-Changeux model and gives a rate equation with 240 denominator terms. Discussion in terms of K and V effects is not possible. A simplified version of the mechanism can be shown to give v-versus-[S] curves that are either sigmoid or non-sigmoid. They may show substrate inhibition or no final maximum, and the double-reciprocal plots can be concave up or down. The corresponding binding model is determined by only two constants and gives a linear double-reciprocal plot. The substrate-modifier mechanism is a simple example of a mechanism where inclusion of catalytic steps leads to a genuine increase in degree of the rate equation. The v-versus-[S] curve can show such complexities as two maxima and a minimum, and the double-reciprocal plot can cross its asymptote twice, proving the rate equation to be 4:4. A simplified version is 3:3, and analysis shows that at least 18 of the 27 double-reciprocal plots that can arise with 3:3 functions are possible with this particular mechanism. Representative double-reciprocal and Scatchard plots are presented for several sets of rate-constant values. It is concluded that relatively simple mechanisms give pseudo-steady-state rate equations of high degree and considerable complexity. With extended ranges of substrate concentrations there is every reason to believe that experimental data would show the sort of deviations from Michaelis-Menten kinetics seen with calculated curves for such simple mechanisms. Narrow ranges of substrate concentration, on the other hand, would lead to inflexions and curvature being overlooked. It is not possible to discuss such deviations from Michaelis-Menten kinetics in terms of kinetic constants such as Km and V, and, in general, it is also difficult to see any simple way to explain intuitively such features as sigmoidicity, substrate inhibition, double-reciprocal convexity and decrease in degree by cancellation of common factors between numerator and denominator of rate equations. These conclusions apply with even more force when catalytic steps are included, for then the rate equations, are for multi-site mechanisms, of higher degree, allowing increasingly complex curve shapes. A number of enzymes were studied and initial-rate data were fitted by computer.(ABSTRACT TRUNCATED AT 400 WORDS)

Pig heart fumarase really does exhibit negative kinetic co-operativity at a constant ionic strength

“…This conclusion seems to be at odds with the studies by Alberty and co-workers (Alberty & Bock, 1953;Alberty et a!., 1954;Taraszka & Alberty, 1964) and themore recent study by Bardsley et al (1980). Although Andersen (1980) and Wharton & Szawelski (1982) were careful to prepare substrate solutions of the correct pH, neither of these studies appears to have maintained a constant ionic strength as the substrate concentration was increased.…”

“…Negative co-operativity can usually be accommodated (Alberty & Bock, 1953;Taraszka & Alberty, 1964;Segel, 1975;Neet, 1980;Bardsley et al, 1980) (1). However, mechanism (2) does provide a useful set ofparameters for comparative purposes.…”

A novel approach for enhancing the catalytic efficiency of a protease at low temperature: Reduction in substrate inhibition by chemical modification

“…Enzyme inhibition by high substrate concentrations commonly causes departures from Michaelis-Menten kinetics (Bardsley et al, 1980), and as a result limits many industrial bioconversion processes (Burton et al, 2002). For example an important enzyme used in the diary industry (b-galactosidase from Kluyveromyces lactis) was immobilized and shown (by enzyme kinetic studies) to have diminished specific activity but enhanced productivity as a result of reduced noncompetitive product inhibition with respect to glucose (Mateo et al, 2004a).…”

Multiple Binding Sites for Substrates and Modulators of Semicarbazide-Sensitive Amine Oxidases: Kinetic Consequences

“…With both BPAO and hSSAO, oxidation proceeds by a ping-pong bi-ter process. Although methodologies are available that could generate substrate inhibition equations in such systems, these involve complex mathematics (Bardsley et al, 1980;Segel, 1993) that become unmanageable when terms describing regulators acting at multiple sites are introduced. ak p E + P Scheme 2.…”