ABO Transferase
Definition
A glycosyltransferase enzyme encoded by the ABO gene on chromosome 9. The A allele encodes an enzyme that adds N-acetylgalactosamine to H antigen, creating A antigen. The B allele encodes an enzyme that adds galactose, creating B antigen. The O allele encodes a non-functional form.
- Gene location
- Chromosome 9
- A allele product
- Adds N-acetylgalactosamine to H antigen
- B allele product
- Adds galactose to H antigen
- O allele
- Produces a non-functional enzyme
- Substrate
- H antigen
Common questions
Why does the O allele fail to produce an antigen?+
A frameshift mutation truncates the enzyme so it cannot transfer any sugar onto the H antigen, leaving the H antigen chemically unmodified.
How does this enzyme relate to bloodstain serology?+
Classic serological ABO typing detects the A and B antigens these enzymes produce on red cells, not the enzyme itself; modern forensic casework has largely moved to DNA-based STR or SNP typing instead.
Can a person carry both the A and B transferase genes?+
Yes, an AB heterozygote produces both enzymes, so both A and B antigens appear on the red cell surface at the same time.
Related terms
- Bombay Phenotype (Oh)
- A rare phenotype in which individuals lack functional H antigen on red cells and in secretions due to mutations in FUT1 (and...
- Forward Grouping (Cell Grouping)
- The direct test of red blood cells with known anti-A and anti-B reagent antibodies to determine which ABO antigens are present on...
- 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...
- Reverse Grouping (Serum Grouping)
- Testing a person's serum against known A1 and B reagent red cells to identify which antibodies are present. A healthy adult with...
- Secretor Status
- A genetic trait that determines whether a person expresses their ABO blood group antigens in secreted body fluids such as saliva, semen,...