Practice question

Blood group oligosaccharide construction depends nucleotide sugar utilizing glycosyltransferases retaining mechanism not phosphoinositide hydrolyzing enzymes that cleave glycerophosphate bonds. Formation H requires GDP fucose dependent FUT1 FUT2 FUT2 secretor adding fucose alpha one two linkage Gal. Conversion A uses UDP GalNAc dependent alpha one three N acetylgalactosaminyltransferase GTA adding GalNAc, B uses UDP Gal dependent galactosyltransferase GTB adding galactose both GT6 family retaining via SNi like mechanism. These catalyze glycosidic bond formation with retention stereochemistry requiring manganese. Phospholipase C isozymes PLC beta gamma delta epsilon hydrolyze phosphatidylinositol four five bisphosphate at glycerophosphate bond generating diacylglycerol activating PKC RasGRP and inositol trisphosphate releasing calcium via IP3 receptors ER. Its active site X Y domains bind calcium C2 domain distinct GT fold Rossmann. Thus PLC participates calcium signaling downstream GPCR RTK not glycan anabolism. Confusing PLC glycosyltransferases mixes two lipid pathways. Understanding enzymatic classification helps predict inhibition U73122 for PLC versus substrate analogs for blood group enzymes separating immunogenetics second messenger biology important biochemistry exams distinguishing transferase versus hydrolase reactions and metabolic contexts and physiological roles.