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Keywords:

  • biofuels;
  • free radicals;
  • hydrolysis reactions;
  • metalloproteins;
  • radical traps

In this Communication the authors characterized the decarbonylation reaction catalyzed by cyanobacterial aldehyde decarbonylase (cAD) as being independent of oxygen. Further experiments have now led the conclusion that the possibility that the observed activity was due to trace amounts of oxygen in the reaction buffer cannot be excluded.

The difficulties in establishing the dependence of the reaction on molecular oxygen stem, in part, from the very low activity of the enzyme under either aerobic or anaerobic conditions. It was found that oxygen scrubbing systems that are routinely employed to remove oxygen from biochemical reactions, such as sodium dithionite, glucose oxidase/glucose and protocatechuate dioxygenase/protocatechuate, are ineffective at decreasing the activity of cAD using the assay conditions described in this Communication, even when included in large excess. Although these observations support the initial assertion that oxygen was not involved, when the assays were performed in an anaerobic chamber capable of maintaining oxygen at very low concentrations, i.e. below 0.5 ppm, (which was not available at the time of the original experiment) very little activity was now observed.

Given this discrepancy, the involvement of molecular oxygen in the cAD-catalyzed reaction cannot be unambiguously ruled out.

While the data and conclusions in the rest of the paper remain unaltered, the tentative mechanism presented for the enzyme activity will obviously need to be reconsidered.