Malcolm Dixon (18 April 1899 – 7 December 1985) was a British biochemist.

Education and early life

Dixon was born in

Cambridge Cambridge ( ) is a List of cities in the United Kingdom, city and non-metropolitan district in the county of Cambridgeshire, England. It is the county town of Cambridgeshire and is located on the River Cam, north of London. As of the 2021 Unit ...

, England, to Allick Page Dixon and Caroline Dewe Dixon (née Mathews). He was educated at home (having come down with

tuberculosis Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is a contagious disease usually caused by ''Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can al ...

aged 12) and at

Emmanuel College, Cambridge Emmanuel College is a constituent college of the University of Cambridge. The college was founded in 1584 by Sir Walter Mildmay, Chancellor of the Exchequer to Elizabeth I. The site on which the college sits was once a priory for Dominican mo ...

, where he graduated with a BA in Natural Sciences in 1921 and was later an 1851 Exhibition Senior Student.) He was awarded his

PhD A Doctor of Philosophy (PhD, DPhil; or ) is a terminal degree that usually denotes the highest level of academic achievement in a given discipline and is awarded following a course of graduate study and original research. The name of the deg ...

in 1925, for research supervised by

Frederick Gowland Hopkins Sir Frederick Gowland Hopkins (20 June 1861 – 16 May 1947) was an English biochemist who was awarded the Nobel Prize in Physiology or Medicine in 1929, with Christiaan Eijkman, for the discovery of vitamins. He also discovered the amino ...

Research and career

Dixon's research investigated the purification of

enzymes An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...

and the

enzyme kinetics Enzyme kinetics is the study of the rates of enzyme catalysis, enzyme-catalysed chemical reactions. In enzyme kinetics, the reaction rate is measured and the effects of varying the conditions of the reaction are investigated. Studying an enzyme' ...

of enzyme-catalyzed reactions. He studied the oxidation of

glutathione Glutathione (GSH, ) is an organic compound with the chemical formula . It is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources ...

and other thiols by molecular oxygen and measured the

redox Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...

potential of the thiol-

disulfide In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups. In inorg ...

system, also establishing that the oxidation of glutathione was catalyzed by trace metals. He investigated

xanthine oxidase Xanthine oxidase (XO or XAO) is a form of xanthine oxidoreductase, a type of enzyme that generates reactive oxygen species. These enzymes catalyze the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to ...

, and thereby elucidated many aspects of the chemistry of

dehydrogenase A dehydrogenase is an enzyme belonging to the group of oxidoreductases that oxidizes a substrate by reducing an electron acceptor, usually NAD+/NADP+ or a flavin coenzyme such as FAD or FMN. Like all catalysts, they catalyze reverse as well as ...

s. He showed that the

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

formed in the reaction of xanthine oxidase with molecular oxygen inactivated the enzyme and that the inhibition could be relieved by the addition of

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting ...

, thus helping to establish a biochemical role for the latter enzyme. Dixon published a series of papers on D-amino acid oxidase, detailing the kinetics and thermodynamics of association of the

coenzyme A cofactor is a non-protein chemical compound or Metal ions in aqueous solution, metallic ion that is required for an enzyme's role as a catalysis, catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can ...

with the apoprotein, the substrate and inhibitor specificity, and the effect of pH on the kinetic constants. Dixon was an expert on the theory and use of manometers. In 1931, he collaborated with David Keilin and Robin Hill to determine the first absorption spectrum of a cytochrome, cytochrome c. Dixon studied the chemistry of lachrymators and

mustard gas Mustard gas or sulfur mustard are names commonly used for the organosulfur compound, organosulfur chemical compound bis(2-chloroethyl) sulfide, which has the chemical structure S(CH2CH2Cl)2, as well as other Chemical species, species. In the wi ...

and proposed a phosphokinase theory to explain their mode of action. Dixon proposed a widely used way of plotting enzyme inhibition data, commonly known as the ''Dixon plot'', in which reciprocal rate is plotted against the inhibitor concentration. Rather confusingly, the same name is sometimes given to a quite different plot proposed by Dixon in the same year for analysing pH dependences, in which the logarithm of a Michaelis–Menten parameter is plotted against pH.

''Enzymes'' (Dixon & Webb)

Dixon's classic book ''Enzymes'', written with Edwin C. Webb and published in 1958, with further editions in 1964 and 1979, had a great influence of the development of biochemistry. It contained one of the first major efforts to devise a systematic way of classifying and naming enzymes. This formed the starting point for the present classification by the IUBMB.Nomenclature Committee of the International Union of Biochemistry and Molecular Biology, Enzyme Nomenclature: https://www.qmul.ac.uk/sbcs/iubmb/enzyme/

Awards and honours

Dixon was elected a Fellow of the Royal Society (FRS) in 1942 and became a Fellow of

King's College, Cambridge King's College, formally The King's College of Our Lady and Saint Nicholas in Cambridge, is a List of colleges of the University of Cambridge, constituent college of the University of Cambridge. The college lies beside the River Cam and faces ...

in 1950. He died in Cambridge in 1985.

References

{{DEFAULTSORT:Dixon, Malcolm British biochemists Fellows of the Royal Society Alumni of Emmanuel College, Cambridge Fellows of King's College, Cambridge 1899 births 1985 deaths Scientists from Cambridge