4-amino-5-hydroxymethyl-2-methyl-pyrimidine phosphate kinase (HMPP-kinase) catalyzes two consecutive phosphorylation steps in the thiamine phosphate biosynthesis pathway, leading to the synthesis of vitamin B1. The first step is the phosphorylation of the hydroxyl group of HMP to form 4-amino-5-hydroxymethyl-2-methyl-pyrimidine phosphate (HMP-P) and then the phophorylation of HMP-P to form 4-amino-5-hydroxymethyl-2-methyl-pyrimidine pyrophosphate (HMP-PP), which is the substrate for the thiamine synthase coupling reaction.
Jiyao W et al.(2023). "The conserved domain database in 2023.",