Isoenzyme (Isozyme)
Definition
Multiple molecular forms of the same enzyme that differ in amino acid sequence but catalyse the same reaction. In forensic serology, isoenzyme patterns in bloodstains can be resolved by gel electrophoresis and compared to reference samples for individualisation. Useful when DNA is too degraded for profiling.
- Also called
- Isozyme
- Separation method
- Gel electrophoresis
- Forensic use
- Bloodstain individualisation before DNA typing
- Value when DNA fails
- Usable on degraded samples with residual enzyme activity
Common questions
How is an isoenzyme pattern different from a DNA profile?+
An isoenzyme pattern reflects protein forms encoded by different alleles at an enzyme-coding locus, visualised by their electrophoretic mobility and activity staining, not by direct sequence comparison. It gives a phenotype, a coarser and less individualising result than a modern STR or SNP DNA profile.
Why is isoenzyme typing rarely used in current casework?+
Enzyme activity degrades faster than DNA in aged or environmentally exposed stains, and the discrimination power of a handful of polymorphic enzyme systems is far lower than multiplex STR typing. It survives mainly as a historical technique relevant to reviewing old case files.
Related terms
- Amino Acid
- The monomer unit of proteins. All 20 standard amino acids share a central carbon bonded to an amino group, a carboxyl group,...
- Haemoglobin
- The iron-containing oxygen-transport protein in red blood cells, composed of four polypeptide subunits each with a haem prosthetic group. Its pseudoperoxidase activity...
- Peroxidase
- An enzyme that catalyses the transfer of oxygen from hydrogen peroxide to an electron donor, often producing a coloured product. Haemoglobin has...
- Protein Denaturation
- The loss of a protein's three-dimensional structure without breaking peptide bonds, caused by heat, pH change, UV radiation, or chemical agents such...
- Proteolysis
- The hydrolytic cleavage of peptide bonds by proteolytic enzymes (proteases). In biological evidence, proteolysis occurs via endogenous cellular proteases released during autolysis...