Figure 1: Methane oxidation and formaldehyde assimilation.
From: Highly efficient methane biocatalysis revealed in a methanotrophic bacterium
(a) Predicted positions of incorporated 13C (indicted in red) for the EDD (dark red arrows) and the EMP (blue arrows) variants. Dashed lines indicate multistep reactions. The pentose-phosphate pathway variant for regeneration of ribulose 5-phosphate is indicated by orange dashed arrows. Enzyme activities (in nmol min1 per mg protein) in cell free extracts of M. alcaliphilum 20Z were as follows: methane monoxygenase (Mmo), 70±5; PQQ-dependent methanol dehydrogenase (Mdh), 230±12; NAD-dependent formate dehydrogenase (Fdh), 130±7; hexulose phosphate synthase/hexulose phosphate isomerase (Hps/Hpi), 600±30; glucose phosphate isomerase (Gpi), 32±5; NADP-dependent glucose 6-phosphate dehydrogenase, 34±2 (Gpd); NAD-dependent glucose 6-phosphate dehydrogenase, 23±2 (Gdp); NADP-dependent 6-phosphogluconate dehydrogenase (Edd), 32±2; KDPG aldolase (Eda), 60±4; fructose-bisphosphate aldolase (Fba), 35± 2; PPi-phosphofructokinase (Pfk), 70± 4. (b) Summary equations for production of 3-phosphoglycerate from formaldehyde via the RuMP pathway for the EDD variant (1) or the EMP variant with either the ATP-dependent EMP pathway (2) or the PPi-dependent EMP pathway (3). Abbreviations: Ru5P, ribulose 5-phosphate; He6P, 3-hexulose 6-phosphate; F6P, fructose 6-phosphate; KDPG, 2-keto-3-deoxy 6-phosphogluconate; F1,6P, fructose 1,6-bisphosphate; DAP, dihydroxyacetone phosphate; GAP, glyceraldehyde 3-phosphate; PGA, 3-phosphoglycerate; Pi, inorganic phosphate.
