An enzyme basis for blood type A intermediate status.
The blood type A is known to be subclassified as A1, A2, and A1-A2 intermediate (Aint), depending upon red cell agglutinability with anti-A1 and anti-H lectins. Approximately 80% of the blood group H-sites remained unglycosylated in type Aint erythrocyte membranes. Plasma from Aint individuals contains a special blood group GalNAc transferase (UDP-GalNAc:2'-fucosylgalactoside-alpha-3-N-acetylgalactosaminyl transferase), which is different from the enzyme in A1 plasma and the enzyme in A2 plasma. A1-enzyme has strong affinity to UDP-GalNAc and 2'-fucosyllactose, A2-enzyme has low affinity to both substrates, and Aint-enzyme has strong affinity to UDP-GalNAc and very low affinity to 2'-fucosyllactose, which is a soluble analog of the H-substances. The low degree of glycosylation of the blood group H-sites due to the low affinity of Aint-enzyme with the H-substances can account for the lower A activity and higher H activity in Aint red cells than in A1 red cells. The blood group A allele can be subdivided into three common alleles, A1, A2, and Aint, each controlling the formation of different types of blood group GalNAc transferases.
D000017:ABO Blood-Group System / Q000235:genetics*; D000483:Alleles; D004910:Erythrocyte Membrane / Q000201:enzymology; D004912:Erythrocytes / Q000201:enzymology; D005700:Galactosyltransferases / Q000235:genetics*; D005787:Gene Frequency; D006801:Humans; D007700:Kinetics; D017350:N-Acetylgalactosaminyltransferases
D000017:ABO Blood-Group System; D005700:Galactosyltransferases; D017350:N-Acetylgalactosaminyltransferases; C003742:UDPgalactosamine-galactose acetylgalactosaminyltransferase