Recombinant bovine lactoperoxidase as a tool to study the heme environment in mammalian peroxidases

The cDNA encoding bovine lactoperoxidase (LPO) has been expressed in CHO cells. The recombinant LPO was secreted as an enzymatically active single chain molecule presenting two immunoreactive forms of 88 kDa and 82 kDa, differing by their glycosylation. rLPO exhibited the characteristic absorbance spectrum with a Soret peak at 413 nm. Engineering of rLPO into a myeloperoxidase (MPO)-like molecule was attempted by substituting Gln-376 by Met, a residue known to achieve covalent binding with the heme in MPO. However, the resulting bovine LPO mutant failed to acquire the peculiar absorbance spectrum and the chlorinating activity of MPO, underlining the complex nature of interactions in the heme vicinity.