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

Education and early life

Dixon was born in Cambridge, UK to Allick Page Dixon and Caroline Dewe Dixon (née Mathews). He received his PhD 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, even though Casimir Funk, a Po ...

at the

University of Cambridge , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledge. , established = , other_name = The Chancellor, Masters and Schola ...

Research and career

Dixon's research investigated the purification of

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

and the

enzyme kinetics Enzyme kinetics is the study of the rates of 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's kinetics in th ...

of enzyme-catalyzed reactions. He studied the oxidation of

glutathione Glutathione (GSH, ) 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 such as reactive oxygen species, free radicals, pero ...

and other

thiols In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

by molecular oxygen and measured the

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

potential of the thiol-

disulfide In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

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

xanthine oxidase Xanthine oxidase (XO, sometimes 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 xanthin ...

, 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 f ...

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 viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

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 t ...

, thus helping to establish a biochemical role for the latter enzyme. Dixon published a series of papers on D-amino acid

oxidase In biochemistry, an oxidase is an enzyme that catalyzes oxidation-reduction reactions, especially one involving dioxygen (O2) as the electron acceptor. In reactions involving donation of a hydrogen atom, oxygen is reduced to water (H2O) or hydro ...

, detailing the kinetics and thermodynamics of association of the

coenzyme A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's role as a catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can be considered "helper molecules" that ass ...

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 David Keilin FRS (21 March 1887 – 27 February 1963) was a Jewish scientist focusing mainly on entomology. Background and education He was born in Moscow in 1887 and his family returned to Warsaw early in his youth. He did not attend scho ...

and Robin Hill to determine the first absorption spectrum of a cytochrome,

cytochrome c The cytochrome complex, or cyt ''c'', is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins and plays a major role in cell apoptosis. Cytochrome c is hig ...

. Dixon studied the chemistry of

lachrymator Tear gas, also known as a lachrymator agent or lachrymator (), sometimes colloquially known as "mace" after the early commercial aerosol, is a chemical weapon that stimulates the nerves of the lacrimal gland in the eye to produce tears. In ad ...

s and

mustard gas Mustard gas or sulfur mustard is a chemical compound belonging to a family of cytotoxic and blister agents known as mustard agents. The name ''mustard gas'' is technically incorrect: the substance, when dispersed, is often not actually a gas, b ...

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 The International Union of Biochemistry and Molecular Biology (IUBMB) is an international non-governmental organisation concerned with biochemistry and molecular biology. Formed in 1955 as the International Union of Biochemistry (IUB), the union ...

.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 is a constituent college of the University of Cambridge. Formally The King's College of Our Lady and Saint Nicholas in Cambridge, the college lies beside the River Cam and faces out onto King's Parade in the centre of the city ...

in 1950. He died in Cambridge in 1985.

References

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