Kinetic studies on Korean serum cis-AB enzymes reveal diminished A and B transferase activities

Background: cis-AB enzymes are rare glycosyltransferases that synthesize both blood group A and B antigens. We have identified a large cohort of Korean cis-AB blood donors and studied the N-acetylgalactosaminyltransferase (glycosyltransferase A, GTA) and galactosyltransferase (glycosyltransferase B, GTB) activity of their cis-AB serum enzymes. Materials and methods: The ds-ABO1 allele was identified by PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) in 60 donors collected at the Gwangju-Chonnam Red Cross Blood Center. Enzyme assays of this cis-AB enzyme were performed on available serum samples from 16 donors with the cis-ABO1/O genotype and three with the cis-ABO1/A genotype. Results: In cis-AB donors with an O allele, both the GTA and GTB activity of the cis-AB enzyme were markedly reduced compared to normal A and B controls (29% and 27%, respectively). This is consistent with the behaviour predicted from kinetic studies of a recombinant model of the corresponding AAAB enzyme. Conclusion: Although variable, cis-AB enzymes feature reduced GTA and GTB activities. Summary: Cis-AB enzymes feature variable but reduced GTA and GTB activities with relatively weaker GTB activity, consistent with the weak agglutination present on forward typing with anti-B.