InterPro domain: IPR017552

6-phospho 3-hexuloisomerase (PHI, also known as rmpB) is part of the ribulose monophosphate (RuMP) pathway, which in one direction removes the toxic metabolite formaldehyde by assimilation into fructose-6-phosphate [ 1 ]. In the other direction, in species lacking a complete pentose phosphate pathway, the RuMP pathway yields ribulose-5-phosphate, necessary for nucleotide biosynthesis, at the cost of also yielding formaldehyde. These latter species tend usually have a formaldehyde-activating enzyme to attach formaldehyde to the C1 carrier tetrahydromethanopterin.

1. A novel operon encoding formaldehyde fixation: the ribulose monophosphate pathway in the gram-positive facultative methylotrophic bacterium Mycobacterium gastri MB19. J. Bacteriol. 182, 944-8