Biosynthesis of Pyridoxal Phosphate STEPS 1-2 OF FIGURE 25.1:OXIDATION Biosynthesis of pyridoxal phosphate begins with oxidation of aldehyde group in D-erythrose 4-phosphate to give D- erythronate 4-phosphate Requires NAD+as cofactor Cysteine-SH group in enzyme adds to aldehyde carbonyl group of D-erythrose 4-phosphate to give intermediate hemithioacetal Hemithioacetal is oxidized by NAD+to a thioester Hydrolysis of thioester yields erythronate 4-phosphate STEPS 1-2 OF FIGURE 25.1: OXIDATION Biosynthesis of pyridoxal phosphate begins with oxidation of aldehyde group in D-erythrose 4-phosphate to give D￾erythronate 4-phosphate ▪ Requires NAD+ as cofactor ▪ Cysteine –SH group in enzyme adds to aldehyde carbonyl group of D-erythrose 4-phosphate to give intermediate hemithioacetal ▪ Hemithioacetal is oxidized by NAD+ to a thioester ▪ Hydrolysis of thioester yields erythronate 4-phosphate Biosynthesis of Pyridoxal Phosphate