**2. Grouping of isozymes**

Isozymes are divided into three categories depending on the way they are biosynthesized:


The distinction between multiple alleles and multiple gene loci as causes of isozyme formation is that multiple alleles are the result of differences between individual members

Fig. 1. A photograph of the result obtained by vertical starch-gel electrophoresis (approx. 19 hr. at 5v/cm.) with serum samples from six healthy individuals. Only the section of gel from the sample slots to the albumin is included in the photograph. Samples 1 and 2 are from female identical twins, 45 years old. Samples 3-5 are from 9-year-old female non-identical

Isozymes are divided into three categories depending on the way they are biosynthesized: 1. isoenzymes (multilocus isozymes) arise from multiple gene loci, which code for

2. allozymes (or alleloenzymes), are structurally distinct variants of a particular

3. secondary isozymes result from post-translational modifications of the enzyme

The distinction between multiple alleles and multiple gene loci as causes of isozyme formation is that multiple alleles are the result of differences between individual members

quadruplets and sample 6 is from their mother. (Smithies, 1958)

structurally distinct polypeptide chains of the enzyme;

polypeptide chain, coded by multiple alleles at a single locus;

**2. Grouping of isozymes** 

structure;

of a certain species, whereas multiple loci are common to all members of a species (Markert, 1975.).

The most probable reason for the presence of multilocus enzyme forms is the gene duplication. The gene duplication — the multiplication of genes in the genom —can come into existence by, for example, not equal crossing over. The frequency of mutation of various structural genes can be different, as a result of which some genes only rarely present in different allelic variant, as more alleles present in the population of other isoforms. This difference can be accepted as the evidence of a separate locus.

For the formation of multilocus isoforms a different evolutionary way can be imagined. It is probable, that the variation of the structural genes of originally different enzymes can cause the formation of similar catalytic functions. (H. Nagy, 1999).

Enzymes with variable substrates generally show higher variability itseves (catechol oxidase, acid phosphatase, peroxidase, esterase), but the amount of allozymic polymorphism is an increasing function of environmental variation. "Observations on natural pupulatians are cited which substantiate the claim that allozymic polymorphism is primarily due to selection acting on environmental variation in gene function. …a large portion of the observed allozymic variation is due to a rather specific type of phenomenon: substrate variability" (Gillespie and Langley, 1974).

Enzymes with a single, special substrate show lower variability (glucose phosphate isomerase, phosphoglucomutase, glutamate-oxalacetate transaminase, glucose-6-phosphate transaminase etc.), but the banding patterns are less affected by the environment (Gillespie and Kojima, 1968; Gillespie and Langley, 1974).
