In biochemistry, isozymes (or isoenzymes) are isoforms (closely related variants) of enzymes. In many cases, they are coded for by homologous genes that have diverged over time. Although, strictly speaking, allozymes represent different alleles of the same gene, and isozymes represent different genes whose products catalyse the same reaction, the two words are usually used interchangeably. Biochemistry is the chemistry of life, a bridge between biology and chemistry that studies how complex chemical reactions give rise to life. ... In biology, a protein isoform is a version of a protein with some small differences, usually a splice variant or the product of some posttranslational modification. ... Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... Homology is an important concept in several disciplines: Homology (anthropology) in archaeology and anthropology. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... In chemistry and biology, catalysis (in Greek meaning to annul) is the acceleration of the rate of a chemical reaction by means of a substance, called a catalyst, that is itself unchanged chemically by the overall reaction. ...

Introduction

Isozymes were first described by Hunter and Markert (1957) who defined them as different variants of the same enzyme having identical functions and present in the same individual. This definition encompasses (1) enzyme variants that are the product of different genes and thus represent different loci (described as isozymes) and (2) enzymes that are the product of different alleles of the same gene (described as allozymes). Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... The word locus (plural loci) is Latin for place. In biology, a locus is the position of a gene (or other significant sequence) on a chromosome. ... An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ...

Isozymes are usually the result of gene duplication, but can also arise from polyploidisation or hybridization. Over evolutionary time, if the function of the new variant remains identical to the original, then it is likely that one or the other will be lost as mutations accumulate, resulting in a pseudogene. However, if the mutations do not immediately prevent the enzyme from functioning, but instead modify either its function, or its pattern of gene expression, then the two variants may both be favoured by natural selection and become specialised to different functions. For example, they may be expressed at different stages of development or in different tissues. Schematic of a region of a chromosome before and after a duplication event Gene duplication occurs when an error in DNA replication leads to the duplication of a region of DNA containing a (generally functional) gene. ... Polyploid (in Greek: πολλαπλόν - multiple) cells or organisms contain more than two copies (ploidy) of their chromosomes. ... In genetics, hybridisation is the process of mixing different species or varieties of organisms. ... This article is about mutation in biology, for other meanings see: mutation (disambiguation). ... A pseudogene is a nucleotide sequence that is part of the DNA or an organism that appears to have once coded a gene product (typically a protein) but no longer does so. ... Gene expression (also protein expression or often simply expression) is the process by which a genes information is converted into the structures and functions of a cell. ... Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. ...

Allozymes may result from point mutations or from insertion-deletion (’’indel’’) events that affect the DNA coding sequence of the gene. As with any other new mutation, there are three things that may happen to a new allozyme: A point mutation is a type of mutation that causes the replacement of a single base pair with another pair. ... Mutations are permanent, sometimes transmissible (if the change is to a germ cell) changes to the genetic material (usually DNA or RNA) of a cell. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... Mutations are permanent, sometimes transmissible (if the change is to a germ cell) changes to the genetic material (usually DNA or RNA) of a cell. ...

1. It is most likely that the new allele will be non-functional - in which case it will probably result in low fitness and be removed from the population by natural selection.
2. Alternatively, if the amino acid residue that is changed is in a relatively unimportant part of the enzyme, for example a long way from the active site then the mutation may be selectively neutral and subject to genetic drift.
3. In rare cases the mutation may result in an enzyme that is more efficient, or one that can catalyse a slightly different chemical reaction, in which case the mutation may cause an increase in fitness, and be favoured by natural selection.

An allele is any one of a number of viable DNA codings of the same gene (sometimes the term refers to a non-gene sequence) occupying a given locus (position) on a chromosome. ... Fitness in biology refers to individuals ability to propagate its genes. ... Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... The active site of an enzyme is the binding site where catalysis occurs. ... The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. ... Genetic drift is a mechanism of evolution that acts in concert with natural selection to change the characteristics of species over time. ... In chemistry and biology, catalysis (in Greek meaning to annul) is the acceleration of the rate of a chemical reaction by means of a substance, called a catalyst, that is itself unchanged chemically by the overall reaction. ... A chemical reaction is a process involving one, two or more substances (called reactants), characterized by a chemical change and yielding one or more product(s) which are different from the reactants. ... Fitness in biology refers to individuals ability to propagate its genes. ... Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. ...

An example of an isozyme

An example of an isozyme is glucokinase, a variant of hexokinase which is not inhibited by glucose 6-phosphate. Its different regulatory features and lower affinity for glucose (compared to other hexokinases), allows it to serve different functions in cells of specific organs, such as control of insulin release by the beta cells of the pancreas, or initiation of glycogen synthesis by liver cells. Both of these processes must only occur when glucose is abundant, or problems occur. Glucokinase Glucokinase (EC 2. ... A hexokinase is an enzyme that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate. ... Glucose-6-phosphate (G6P) is a phosphorylated glucose molecule on carbon 6. ... The structure of insulin Red: carbon; green: oxygen; blue: nitrogen; pink: sulfur. ... Beta cells are a type of cell in the pancreas in areas called the islets of Langerhans. ... The pancreas is a retroperitoneal organ that serves two functions: exocrine - it produces pancreatic juice containing digestive enzymes endocrine - it produces several important hormones // Anatomy The pancreas is a retroperitoneal organ located posterior to the stomach on the posterior abdominal wall. ... Glycogen is the principal storage form of glucose in animal cells. ... The liver is an organ in vertebrates, including humans. ...

Distinguishing isozymes

Isozymes (and allozymes) are variants of the same enzyme. Unless they are identical in terms of their biochemical properties, for example their substrates and enzyme kinetics, they may be distinguished by a biochemical assay. However, such differences are usually subtle (particularly between ‘’allozymes’’ which are often neutral variants). This subtlety is to be expected, because two enzymes that different significantly in their function are unlikely to have been identified as ‘’isozymes’’. Ribbon diagram of the catalytically perfect enzyme TIM. Factor D enzyme crystal prevents the immune system from inappropriately running out of control. ... In biochemistry, a substrate is a molecule which is acted upon by an enzyme. ... Figure 1: Diagram of a catalytic reaction, showing the energy needed at each stage of the reaction. ... The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. ...

Whilst isozymes may be almost identical in function, they may differ in other ways. In particular, amino acid substitutions that change the electric charge of the enzyme (such as replacing aspartic acid with glutamic acid) are simple to identify by Gel electrophoresis, and this forms the basis for the use of isozymes as Molecular markers. To identify isozymes, a crude protein extract is made by grinding animal or plant tissue with an extraction buffer, and the components of extract are separated according to their charge by gel electrophoresis. Historically, this has usually been done using gels made from potato starch, however, acrylamide gels provide better resolution, and cellulose acetate gels are now (as of 2005) the norm. In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ... Aspartic acid, also known as aspartate, the name of its anion, is one of the 20 natural proteinogenic amino acids which are the building blocks of proteins. ... Glutamic acid or glutamate (the anionic form of glutamic acid) is one of the 20 most common natural amino acids. ... SDS-PAGE autoradiography DNA agarose gel Gel electrophoresis is a group of techniques used by scientists to separate molecules based on physical characteristics such as size, shape, or isoelectric point. ... SDS-PAGE autoradiography DNA agarose gel Gel electrophoresis is a group of techniques used by scientists to separate molecules based on physical characteristics such as size, shape, or isoelectric point. ... Binomial name Solanum tuberosum L. The potato (plural form: potatoes) (Solanum tuberosum) is a perennial plant of the Solanaceae, or nightshade, family, grown for its starchy tuber. ... The chemical compound acrylamide (acrylic amide) has the chemical formula C3H5NO and structure It is a white odorless crystalline, soluble in water, ethanol and ether. ... Cellulose acetate, first prepared in 1865, is the acetate ester of cellulose. ... 2005(MMV) is a common year starting on Saturday of the Gregorian calendar. ...

All the proteins from the tissue are present in the gel, so that individual enzymes must be identified using an assay that links their function to a staining reaction. For example, detection can be based on the localised precipitation of soluble indicator dyes such as tetrazolium salts which become insoluble when they are reduced by cofactors such as NAD or NADP, which generated in zones of enzyme activity. This assay method requires that the enzymes are still functional after separation (native gel electrophoresis), and provides the greatest challenge to using isozymes as a laboratory technique. Yarn drying after being dyed in the early American tradition, at Conner Prairie living history museum. ... Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ... A cofactor is any substance that needs to be present in addition to an enzyme to catalyze a certain reaction. ... Nicotinamide adenine dinucleotide (NAD+) (Note that the adenonosyl sugar is of the wrong absolute configuration in the diagram: it should have the same configuration as the nicotinamide sugar. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ...

Isozymes and allozymes as molecular markers

Population genetics is essentially a study of the causes and effects of genetic variation within and between populations, and in the past isozymes have been amongst the most widely used Molecular markers for this purpose. Although they have now been largely superseded by more informative DNA-based approaches (such as direct DNA sequencing, Single nucleotide polymorphisms and microsatellites), they are still amongst the quickest and cheapest marker systems to develop, and remain (as of 2005) an excellent choice for projects that only need to identify low levels of genetic variation, e.g. quantifying mating systems. Population genetics is the study of the distribution of and change in allele frequencies under the influence of the five evolutionary forces: natural selection, genetic drift, mutation, migration and nonrandom mating. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ... For the sense of sequencing used in electronic music, see the music sequencer article. ... A Single Nucleotide Polymorphism or SNP (pronounced snip) is a DNA sequence variation, occurring when a single nucleotide: adenine (A), thymine (T), cytosine (C) or guanine (G) - in the genome is altered. ... A microsatellite is a short, noncoding DNA sequence (a Tandemly Repetitive DNA sequence) that is repeated many times within the genome of an organism. ... 2005(MMV) is a common year starting on Saturday of the Gregorian calendar. ... In sociobiology and behavioural ecology, the term mating system is used to describe the ways in which animal societies are structured in relation to sexual behaviour. ...

References

• Hunter, R. L. and C.L. Merkert. (1957) Histochemical demonstration of enzymes separated by zone electrophoresis in starch gels. Science125: 1294-1295
• Wendel, JF, and NF Weeden. 1990. Visualisation and interpretation of plant isozymes. Pp. 5-45 in D. E. Soltis and P. S. Soltis, eds. Isozymes in plant biology. Chapman and Hall, London.
• Weeden, NF, and JF Wendel. 1990. Genetics of plant isozymes. Pp. 46-72 in D. E. Soltis and P. S. Soltis, eds. Isozymes in plant biology. Chapman and Hall, London
• Crawford, DJ. 1989. Enzyme electrophoresis and plant systematics. Pp. 146-164 in D. E. Soltis and P. S. Soltis, eds. Isozymes in plant biology. Dioscorides, Portland, Oregon.
• Hamrick, JL, and MJW Godt. 1990. Allozyme diversity in plant species. Pp. 43-63 in A. H. D. Brown, M. T. Clegg, A. L. Kahler and B. S. Weir, eds. Plant Population Genetics, Breeding, and Genetic Resources. Sinauer, Sunderland

External links

• Allozyme Electrophoresis Techniques - a complete guide to starch gel eletrophoresis