A red blood cell's ABO type comes from short sugar chains (antigens) sitting on the surface of its membrane. Type A carries an extra N-acetylgalactosamine cap, type B an extra galactose cap, type AB carries both, and type O carries neither — which is why type O is the "universal donor": no A/B antigen means no A/B antibody in a recipient's plasma can attack it.
Specific glycosidase enzymes (e.g. bacterial FpGalNAc-deacetylase/FpGalactosaminidase pairs, or α-galactosidase for B) can cleave these caps off intact, living red cells without damaging them — a real strategy explored to convert donated A/B/AB blood into universal O supply. This simulator models that cleavage per red cell with standard Michaelis-Menten enzyme kinetics:
dC/dt = −Vmax · C / (Km + C)
Vmax = kcat · [E] · f(T)
f(T) = exp( −(T − 37)² / (2·σ²) ), σ ≈ 8 °C
C is the remaining antigen density on a cell (1.0 = untouched, 0 = fully cleaved), [E] is the enzyme dose you set, and f(T) is a bell-shaped thermal-efficiency curve peaking at physiological 37 °C — too cold and the enzyme barely turns over, too hot and it starts to denature. Because the rate is proportional to C at low antigen levels, the last traces of antigen clear the slowest — exactly the long "tail" real enzymatic conversion protocols fight against before a unit is certified antigen-negative.
- Sample composition — pick a pure A/B/AB donor unit or a mixed pool to convert.
- Glycosidase dose — raises Vmax; more enzyme clears antigen faster (and more green enzyme particles appear in the dish).
- Incubation temperature — moves you along f(T); watch conversion stall well off 37 °C.
- Donor compatibility — a stricter, nonlinear readout: even a small residual antigen fraction still risks an immune reaction, so compatibility only approaches 100% once cleavage is nearly complete.