AN ENZYME BASIS FOR BLOOD TYPE-A INTERMEDIATE STATUS

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 34  (6) , 919-924
Abstract
The blood type A is known to be subclassified as A1, A2 and A1-A2 intermediate (Aint), depending on 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 3 common alleles, A1, A2 and Aint, each controlling the formation of different types of blood group GalNAc transferases.