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Table 1 Enzyme activities in cell-free extracts of Clostridium cellulolyticum wild-type and mutant cultures

From: Combined inactivation of the Clostridium cellulolyticum lactate and malate dehydrogenase genes substantially increases ethanol yield from cellulose and switchgrass fermentations

Strain Specific activity (U/mg)
  MDH ME LDH
Wild-type 1.66 ± 0.088 0.30 ± 0.020 < 0.007
Ccel_0137::LtrB (mdh) 0.47 ± 0.056** 0.25 ± 0.013* ND
Ccel_2485::LtrB (ldh) 1.54 ± 0.36 0.29 ± 0.019 NA
(ldh mdh) NA** 0.44 ± 0.019** < 0.055
  1. Mean and standard deviations of enzymatic specific activities are shown from at least three replicate assays. Continuous spectrophotometric assays were performed aerobically at ambient temperature (22°C), using 10 to 20 μg of protein sample in 1-ml reaction mixtures; 1 U of activity catalyzed the oxidation of 1 μmol of NAD(P)H per minute (MDH and LDH), or the reduction of 1 μmol of NADP+ per minute (ME). Specific activities were corrected for substrate-independent NAD(P)H oxidation. Malate dehydrogenase (MDH, EC 1.1.1.37) and malic enzyme (ME, EC 1.1.1.40) activities were measured as described in the Methods section, using NADH and NADP+ cofactors, respectively. No MDH activity was detected in the ldh mdh extracts (NA). Lactate dehydrogenase (LDH, EC 1.1.1.27) activity was determined as for MDH activity, using 1 mM pyruvate, 1 mM fructose-1,6-diphosphate and 0.2 mM NADH. No pyruvate-dependent NADH oxidation was detected in any sample: limits of detection are shown for wild-type and ldh mdh extracts.
  2. Values significantly different from wild-type activity (*P < 0.05; **P < 0.005) were calculated using analysis of variance (ANOVA).
  3. ND = not determined.