Page 183 - The Manga Guide to Biochemistry

Glucosyltransferase determines blood type

Remember when we solved the blood type mystery (in Chapter 3)?
When we were trying to figure out what determines blood type, we discovered

that it was the work of an enzyme.

I remember!
The ABO blood group system is classified according to the differences between

the “sugar chains” on the surface of red blood cells. A sugar chain is a collection of
monosaccharides connected together!

And the differences between those chains are the monosaccharides at the tips, right?

Yeah! For people with Type A blood, that monosaccharide is N-acetylgalactosamine
(GalNAc); for people with Type B blood, it’s galactose (Gal); and for people with Type
O blood, there is no monosaccharide at the tip.

(After writing such a detailed report for the professor, I’ll probably remember
that for the rest of my life...)

That’s correct. The particular monosaccharide that’s attached to the tip of a sugar
chain (or the lack of one) is determined by a certain gene.

Genes are like the “blueprints” for proteins. (Remember: An enzyme is a type of
protein.)

So what really determines blood type is the gene that creates glycosyltransferase,
which is the enzyme that attaches a particular monosaccharide to the tip of a sugar
chain found on the surface of the red blood cell.

So glycosyltransferase attaches a certain monosaccharide, and the type of that
monosaccharide determines blood type?

That’s right. Look again at the structure of the sugar chain of each blood type.

Enzymes Are the Keys to Chemical Reactions 169