HYDROGENASE ENCAPSULATION INTO RED-BLOOD-CELLS AND REGENERATION OF ELECTRON-ACCEPTOR

Biochemical decompression has been proposed as a method for reducing t he amount of time required for deep-sea divers to return to the surfac e. Divers breathing H-2/O-2 mixtures would be presented with hydrogena se enzyme, and decompression would be accelerated by means of the enzy mic removal of excess H-2 from the tissues. We have studied FAD as a h ydrogenase electron acceptor that is capable of transferring electrons derived from Hz oxidation directly to O-2. Kinetic activity constants for the soluble hydrogenase from the bacterium Alcaligenes eutrophus H16 were determined with FAD, FMN and riboflavin as electron accepters , and these, values were compared with those obtained with the physiol ogical electron acceptor NAD(+). The Michaelis constants (K-m) were si milar for FAD, FMN and NAD. However, the maximal catalytic-centre acti vity (k(cat)) was much lower for the flavins, and the catalytic effici ency (k(cat)/K-m) with FAD was 1/20th the value for NAD(+). After enzy me-catalysed FAD reduction to FADH(2), the FAD could be regenerated by addition of O-2 and reduced again by the enzyme in the presence of H- 2. Thus FAD sewed as a regenerable electron shuttle between H-2 and O- 2, H2O2, a by-product of FADH(2) oxidation by O-2, inhibited the enzym e. Much greater inhibition was observed with the reduced form of the e nzyme. Active hydrogenase was efficiently encapsulated into human and pig red blood cells. Hydrogen consumption was seen with lysed carrier cells, but was demonstrated with unlysed carrier cells only when FAD w as co-encapsulated along with enzyme. These results demonstrate that r ed blood cells encapsulating hydrogenase and FAD act as a system for c ontinuous Hz consumption in a mammalian tissue without addition of exo genous factors, and such cells may provide a biotherapeutic method for reducing the risk and treatment of decompression sickness.