Purification and characterization of hydroperoxidase II of Escherichia coli B

The second heme-containing hydroperoxidase isozyme (HP-II) has been isolated from aerobic cultures of Escherichia coli B. The protein exists as a stable tetramer of subunits of equal size, with a combined molecular weight of 312,000. The heme spectrum of HP-II is unusual, in that it exhibits two absorbance maxima at 407 and 591 nm; the alkaline pyridine hemochromogen spectrum shows maxima at 425, 559, and 609 nm. HP-II differs in several respects from the HP-I isozyme previously reported (Claiborne, A., and Fridovich, I. (1979) J. Biol. Chem. 254, 4245-4252). Thus HP-II is virtually devoid of peroxidatic activity toward o-dianisidine but has a 6-fold higher catalatic activity than HP-I. Antisera to HP-II do not cross-react with HP-I, and analyses of chymotryptic and cyanogen bromide digests suggest differences in primary structure between these two isozymes.