Isolation and characterization of protoporphyrin glycoconjugates from rat harderian gland by HPLC, capillary electrophoresis and HPLC/electrospray ionization MS.

It has been widely reported that the Harderian gland, present in most vertebrates, accumulates high levels of porphyrins, particularly protoporphyrin. The present study describes the extraction, identification and characterization of a group of hitherto unreported protoporphyrin glycoconjugates in the rat Harderian gland using HPLC, capillary electrophoresis, on-line HPLC/electrospray ionization MS and tandem MS. The major glycoconjugate was identified as protoporphyrin-1-O-acyl beta-xyloside with a smaller amount of protoporphyrin-1-O-acyl beta-glucoside also detected. In the Harderian glands studied, 50-70% of the porphyrins present were in the form of protoporphyrin glycoconjugates. This is the first reported occurrence of glycoconjugates of porphyrins in Nature and suggests that previous studies have wrongly identified the major porphyrin in the Harderian gland as the unconjugated protoporphyrin.