Also isozymes. Enzymes that catalyse the same reaction, but differ in amino acid sequence, protein structure and kinetics.
Isoforms is the more general term that refers to proteins that share significant similarity, e.g. cytochrome p450s. As most proteins exhibit some sort of catalytic activity, the terms are sometimes interchangeable, but the term isoenzymes are strictly speaking isoforms of a particular enzyme.
Related isoenzymes may share significant sequence homology. Isoenzymes may result from:
- Different genes:
- Completely separate gene products, or
- Differences in sub-units. Some sub-units may be shared.
- Same gene:
- Single nucleotide polymorphism. A base change may be sufficient to cause a change in amino acid sequence which significantly affects the enzyme's kinetics.
- Alternative splicing of the same gene.