As far as I have understood

Isozymes are derived from different genes but perform similar functions

Allozymes are derived from the same gene but different loci, functionally conserved

Isoforms are a result of post transcriptional modification of the same gene, I am not sure for its functional conservation.

Are there anyother things to know about them? Thanks


2 Answers 2


You have the basic idea:

Isozymes come from different genes but carry out the same enzymatic reaction.

Allozymes come from the same gene - i.e., the gene at a particular point on the chromosome; but chromosomes come in pairs, and the allozymes come from the 2 different chromosomes in the pair.

Isoform proteins ["protein variants"] are from the same gene, but they can have the same or different functions, depending on how they are spliced = which exons are included, and in what order. There's a nice picture in the Wikipedia article "protein isoform."

Here are Wikipedia links:

Isozyme - Wikipedia https://en.wikipedia.org/wiki/Isozyme Isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.

Alloenzyme - Wikipedia https://en.wikipedia.org/wiki/Alloenzyme Alloenzymes (or also called allozymes) are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus. ...These are opposed to isozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci.

Protein isoform - Wikipedia https://en.wikipedia.org/wiki/Protein_isoform A protein isoform, or "protein variant" is a member of a set of highly similar proteins that originate from a single gene or gene family and are the result of genetic differences. While many perform the same or similar biological roles, some isoforms have unique functions.


Complementing Helen's answer, I can give one example of isoforms. The main production of nitric oxide in brain is driven by three enzime isoforms of the same gene: neuronal, endothelial and induced Nitric Oxide Synthase (nNOS, eNOS and iNOS). Despite de fact they have their origins from the same gene, they are quite different in terms of regulation and activity. The different isoforms are regulated by different genes and pathways, they are found in different tissues in brain, induced isoform can produce much more NO than the others and, of course, they promote different effects in body physiology, from regulating vital pathways in brain cells to regulation of blood flow.

You could not tell if we're looking at isoforms or allozymes just by analysing their effects in organisms since they both are different forms from same type of enzime, but it's important to know their origins if we want understand how they work.


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