TABLE 1.
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.