| Human lactoperoxidase (LPO) is an enzyme that catalyzes the hydrogen peroxide-mediated oxidation of (pseudo)halides and organic substrates. Its role is as part of the antimicrobial defence system, within the secretions and on the mucosal surfaces where it occurs. LPO is also able to catalyze the oxidation of a wide variety of xenobiotics and endogenous compounds. Recently several single nucleotide polymorphisms (SNPs) of LPO have been identified, and three were investigated in the present study. The variants R414Q, V421M, and R514Q were expressed as C-terminally his-tagged proteins using a plasmid mediated insect cell expression system and purified by affinity chromatography. Recombinant LPO was obtained for all three SNP variants and wild type. Wild type LPO and variant R514Q displayed characteristic LPO absorbance spectra and similar specific activities with ABTS (2,2'-azinobis-[3-ethylbenzthiazoline-6-sulphonic acid]) as substrate. However, variants R414Q and V421M showed no characteristic LPO spectra or peroxidase activity. Results suggest that these variants fail to acquire the heme prosthetic group during biosynthesis due to improper protein folding or due to disruption ofthe local protein environment, which impedes heme incorporation to a significant level. These findings suggest that expression of LPO holoenzyme is sensitive to mutation at these positions and individuals who carry these SNPS may show a deficiency with regard to their expression of active LPO. |
