TABLE 5.

Overview of enzymes involved in pentose biosynthesis in Archaea, Bacteria, and Eukarya

Enzyme	EC no.	Abbreviation	Reaction	Protein superfamily(ies) (according to SCOP)	Protein family(ies)	Distribution
Phosphohexulose isomerase	5.3.1.27	PHI	Fructose 6-phosphate ⇆ d-arabino-3-hexulose 6-phosphate	SIS domain superfamily	Mono-SIS domain family	Archaea (except for some halophiles and Thermoplasmatales), Bacteria (especially methylotrophs)
Hexulose phosphate synthase	4.1.2.43	HPS	d-Arabino-3-hexulose 6-phosphate ⇆ ribulose 5-phosphate + formaldehyde	Ribulose phosphate binding barrel superfamily		Archaea (except for some halophiles and Thermoplasmatales), Bacteria (especially methylotrophs)
Ribose-5-phosphate isomerase	5.3.1.6	RPI	Ribulose 5-phosphate ⇆ ribose 5-phosphate	NagB/RpiA/CoA transferase-like superfamily, ribulose 5-phosphate isomerase lid domain superfamily	d-Ribose-5-phosphate isomerase (RpiA), catalytic domain family; ribulose-5-phosphate isomerase lid domain family	Archaea, Bacteria, Eukarya
Transketolase	2.2.1.1	TK	Sedoheptulose 7-phosphate + d-glyceraldehyde-3-phosphate ⇆ d-ribose 5-phosphate + d-xylulose 5-phosphate	Thiamine diphosphate binding fold (THDP binding), TK C-terminal domain-like	TK-like Pyr module, transketolase C-terminal domain-like	Mca. jannaschii, Thermoplasmatales, Thermococcales, Sulfolobales, Thermoproteales (not in most haloarchaea, other methanogens, and Archaeoglobales), Bacteria, Eukarya
Transaldolase	2.2.1.2	TA	Sedoheptulose 7-phosphate + d-glyceraldehyde 3-phosphate ⇆ d-erythrose 4-phosphate + d-fructose 6-phosphate	Aldolase superfamily	Class I aldolase family	Methanococcus spp., Thermoplasmatales (not in most other Archaea), Bacteria, Eukarya
Glucose 6-phosphate dehydrogenase	1.1.1.49	G6PDH	d-Glucose 6-phosphate + NAD(P)+ → d-glucono-1,5-lactone 6-phosphate + NAD(P)H + H+	N-terminal domain NAD(P) binding Rossman fold-like domain superfamily; C-terminal glyceraldehyde-3-phosphate dehydrogenase-like, C-terminal domain superfamily	GAPDH N-terminal domain family, glucose-6-phosphate dehydrogenase-like family (C-terminal domain)	Bacteria, Eukarya, some Haloarchaea
6-Phosphogluconate dehydrogenase	1.1.1.44	6PGDH	6-Phospho-d-gluconate + NADP+ → d-ribulose 5-phosphate + CO2 + NADPH + H+	NAD(P) binding Rossman fold domains, 6-phosphogluconate dehydrogenase C-terminal domain-like superfamily	6-Phosphogluconate dehydrogenase-like, N-terminal domain family; hydroxyisobutyrate and 6-phosphogluconate dehydrogenase domain family	Bacteria, Eukarya
Ribose 5-phosphate epimerase	5.1.3.1	RPE	d-Ribulose 5-phosphate ⇆ d-xylulose 5-phosphate	Ribulose phosphate binding barrel superfamily	d-Ribulose-5-phosphate 3-epimerase family	Methanococcus spp., Thermoplasmatales (not in most other Archaea), Bacteria, Eukarya