Glycosyltransferase
Definition
The enzyme encoded by the ABO gene locus that attaches terminal sugar residues to the H antigen chain. Group A transferase adds N-acetylgalactosamine; group B transferase adds galactose; group O alleles encode a non-functional enzyme.
- Encoded by
- ABO gene locus
- Function
- Adds terminal sugar to the H antigen chain
- A-type product
- Adds N-acetylgalactosamine
- B-type product
- Adds galactose
- O allele
- Encodes a non-functional enzyme
Common questions
Why does the O blood type lack A or B antigens on red cells?+
The O allele carries a mutation that produces a non-functional or truncated glycosyltransferase, so no terminal sugar is added to the H antigen precursor, leaving type O red cells with neither A nor B antigen.
How does this enzyme explain the AB blood type?+
A person who inherits both the A and B alleles produces both functional transferase variants, so their red cells carry activity that adds both N-acetylgalactosamine and galactose, resulting in both A and B antigens on the same cell population.
Why is understanding this enzyme relevant to forensic blood typing history?+
Before DNA profiling, ABO phenotyping driven by this enzyme was a primary serological method for narrowing suspect pools or associating bloodstains with individuals, even though it could only exclude, not individualise, a source.
Related terms
- Agglutination
- Clumping of red cells that occurs when antibodies in serum bind to incompatible antigens on the cell surface, cross-linking cells into visible...
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Forensic Serology
- The branch of forensic science concerned with detecting and characterising biological fluids (blood, semen, saliva, vaginal secretions) as evidence in legal proceedings,...
- H Antigen
- A fucose-containing oligosaccharide on red cell surfaces and secreted epithelial cells, produced by FUT1 (on red cells) and FUT2 (in secretions). It...
- Isohemagglutinins
- The naturally occurring antibodies (anti-A and/or anti-B) present in serum from birth without prior transfusion or immunisation. Group A individuals carry anti-B;...