Purification and properties of a membrane-bound NADH-cytochrome-b5 reductase from erythrocytes of the sipunculid worm, Phascolopsis gouldii.

The purification to homogeneity of the membrane-bound NADH-cytochrome-b5 reductase from erythrocytes of the sipunculid, Phascolopsis gouldii is reported. This highly purified reductase has allowed more detailed characterizations of its molecular and kinetic properties than was possible in a previous study (Utecht, R.E. and Kurtz, D.M., Jr. (1988) Biochim. Biophys. Acta 953, 164-178). The reductase has a molecular weight of 34,000 and contains FAD as the prosthetic group. In aqueous solution containing 0.5 vol% Triton X-100, the reductase forms an aggregate of Mr approximately 220,000. A higher purity preparation of P. gouldii erythrocyte b5 was also obtained. The combination of purified, solubilized reductase and cytochrome b5 was shown to catalyze the quantitative two-electron reduction of [Fe(III),Fe(III)]methemerythrin to [Fe(II),Fe(II)]deoxyhemerythrin by NADH. The P. gouldii NADH-cytochrome b5 reductase is the first from hemerythrin-containing erythrocytes to be purified and characterized. This methemerythrin reduction system appears to be analogous to methemoglobin reductases from vertebrate erythrocytes.