Table 4

Key PHB production and citric acid cycle enzyme activities in extracts of nitrogen-limiteda R. eutropha cellsc

StrainMean enzyme activity (U/mg protein) ± SDb
PhaAPhaBPhaCMDHCS
H1625 ± 526 ± 268 ± 175.2 ± 1.52.5 ± 0.8
Re241130 ± 615 ± 445 ± 256.0 ± 2.01.4 ± 0.1
  • a Cells were grown in minimal medium containing 0.1 % (wt/vol) NH4Cl and 2% (wt/vol) fructose, as described in Materials and Methods. Nitrogen limitation occurred at 12 to 14 h of culture time. Cells were harvested for enzyme activity determinations 6 to 8 h after the onset of nitrogen limitation.

  • b PhaA, β-ketothiolase; PhaB, acetoacetyl-CoA reductase; PhaC, PHB synthase; MDH, malate dehydrogenase; CS, citrate synthase.

  • c All enzyme activities are defined in U/mg protein. One unit is equivalent to the amount of enzyme needed to convert 1 μmol substrate to product per min at 25°C, except for MDH activity, which is defined as the amount of enzyme needed to convert 1 μmol substrate to product per h at 25°C. All enzyme assays were performed in replicates of three or more.