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. 2010 Aug 24;285(44):33701–33709. doi: 10.1074/jbc.M110.146332

TABLE 1.

Catalytic activities and kinetic parameters of enzymes involved in C5 sugar metabolism

Enzyme activities in cell extracts are those measured under Vmax conditions. S.E on all kinetic parameters are <10% of the mean values. ND, no data.

Enzyme Substrate S. solfataricus
S. acidocaldarius native enzyme (cell extract from xylose-grown cells) activity
Native enzyme (cell extract from xylose-grown cells)
Recombinant enzyme
Km Enzyme activity Km Vmax
mm units/mg protein mm units/mg protein units/mg protein
Xylose dehydrogenase d-Xylose 0.18 0.41 0.18 71 0.25
l-Arabinose 0.47 0.16 0.50 62
Xylonate dehydratase d-Xylonate 0.28a 0.08 ND ND 0.024
l-Arabinonate 0.17a 0.05 ND ND
KDG-aldolase Pyruvate 2.7a 0.13 2.8a 31a 0.07
Glycolaldehyde 2.0a 2.9a
Aldehyde oxidoreductase (DCPIP) Glycolaldehyde 0.37 0.14 ND ND 0.034
Glyoxylate reductase Glyoxylate 5.0 0.54 5.0 150 0.12
NADH+ 0.1 0.1
Malate synthase Glyoxylate 0.05 0.25 0.06 14 0.072
Acetyl-CoA 0.002 0.002
Isocitrate lyase Isocitrate b b 0.96 8 ND
2,5-Dioxopentanoate dehydrogenase (NADP+) Pentanedial ND 0.1 3.3 35 0.15c

a These are apparent Km and Vmax values due to enzyme inhibition in the presence of high substrate concentration.

b Enzyme absent in cell extracts of xylose-grown cells.

c The recombinant enzyme of S. acidocaldarius was characterized as a homotetramer with subunit Mr values = 52,000. When assayed at 70 °C and pH 7.0, Vmax = 50 units/mg and Km = 0.14 mm (pentanedial) and 0.04 mm (NADP+). The specific activity with 2,5, dioxopentanoate (12 mm) was 1.5 units/mg. Enzyme activity was 15-fold higher in cells grown on xylose as compared to glucose.