Deactivation of chloroperoxidase by monosaccharides (d-glucose, d-galactose, and d-xylose)

In this work, it was found that some monosaccharides normally used to stabilize enzymes at high temperatures, however, actually caused a deactivation of chloroperoxidase (CPO). The red native CPO was converted to a stable pale species that lost enzymatic activity. This deactivation was irreversible and was sensitive to temperature. It was different from the general peroxide-mediated deactivation of CPO.Data from measurement of chlorination activity as well as UV–vis, fluorescent, and CD spectral analysis indicated that monosaccharide-induced deactivation can be attributed to precipitation of protein in the presence of monosaccharide and the interaction of the aldehyde group of sugar with amino groups, especially the terminal amino group, on proteins to form Schiff bases which then rearrange to the stable amino ketone.It is further noted that the deactivation efficiency depends on the stereostructure of monosaccharides. d-Glucose was the most efficient inactivating agents due to its aptitude for both of the interactions mentioned in the above paragraphs. The deactivation was specific to aldose. No deprivation of the heme iron was involved in this deactivation.

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► Monosaccharides could cause a suicide inactivation of chloroperoxidase (CPO).
► The sixth axial ligand position of heme iron was occupied by monosaccharides.
► Absorption of Soret band decreased due to occurrence of precipitation of protein.
► Fluorescent and CD spectral analysis indicated a minor uncoiling of α-helix occurred.
► The stereostructure of monosaccharide is related with this enzymatic inactivation.