PURIFICATION AND CHARACTERIZATION OF 2 FORMS OF CYTOCHROME B(5) FROM AN ARACHIDONIC ACID-PRODUCING FUNGUS, MORTIERELLA-HYGROPHILA

Two forms of cytochrome b(5) have been purified from the microsomes of an arachidonic acid-producing fungus, Mortierella hygrophila IFO 5941, after detergent solubilization. They have monomeric molecular masses of about 16 kDa and 19 kDa. Their absorption spectra are similar to those of mammalian cytochrome b(5)s. Their amino acid compositions show some similarity to those of mammalian cytochrome b(5)s, but the contents of some amino acids (glycine, alanine, aspartic acid + asparagine, glutamic acid + glutamine, arginine, proline, histidine, leucine and lysine) are unique to the cytochrome b(5)s of M. hygrophila. Some of their internal peptide sequences also show close homology with those of some mammals (approx. 65 to 67%), while some others show no or little homology. The addition of various acyl-CoAs to NADH-reduced microsomes caused an abrupt shiftdown of the steady state reduction level of cytochrome b(5). This indicates the increased utilization of electrons for the desaturation process and may suggest that the cytochrome b(5)s of this fungus actually take part in its microsomal desaturation system for polyunsaturated fatty acid biosynthesis as electron carriers.