There are 4 different ABO Blood Types: A, B, AB, and O
The gene for the H antigen is locared on Chromosome 19 and encodes for L-fucosyltransferase.
This enzyme places Fucose onto precursor chains on the RBC and on precursor chains in secretions (urine, saliva, plasma, etc).
The genes for the A and B antigens is locared on Chromosome 9 and there are two co-dominant alleles, A and B.
The B allele encodes for D-galactosyltransferase
The A allele encodes for N-acetylgalactosaminyl transferase
These enzymes added a sugar onto the Fucose that was added by the H gene.
ABO type of a person is determined by these sugars on the RBC
A - N-acetylgalactosamine
B - D-galactose
AB - both N-acetylgalactosamine and D-galactose
O - no sugar is added
The ABO blood group system is unique as it is the only one that the body will form antibodies to the antigens. For example, if you are an A you will have antibodies to B. This is why the blood group system is so important. If you were to transfuse B RBCs to an A person, they would destroy them and cause catastrophic problems for the body that may include death. The Blood Banks most important test is to determine the ABO type of recipients and blood donors to ensure that this does not happen.
ABO typing consists of performing an antigen typing of the RBCs (look for the A and/or B antigen) and the reverse typing (look for anti-A and/or anti-B in the plasma). This is how a person's ABO blood type is determined.
ABO type ABO Antigen Typing ABO reverse typing
A A antigen present anti-B present
B B antigen present anti-A present
AB A and B antigen present No ABO antibodies present
O No A or B antigens present anti-A & anti-B present
Picture of the reagents for ABO typing.
In enzymology, a N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase (EC 2.4.1.226) is an enzyme that catalyzes the chemical reaction: UDP-alpha-D-glucuronate + N-acetyl-beta-D-galactosaminyl-(1->4)-beta-D-glucuronosyl- proteoglycan → UDP + beta-D-glucuronosyl-(1->3)-N-acetyl-beta-D-galactosaminyl-(1->4)- beta-D-glucuronosyl-proteoglycan. The 3 substrates of this enzyme are UDP-alpha-D-glucuronate, Chondroitin synthase
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