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 verte brates, accumulates high levels of porphyrins, particularly protoporphyrin. The present study describes the extraction, identification and characteriz ation of a group of hitherto unreported protoporphyrin glycoconjugates in t he rat Harderian gland using HPLC, capillary electrophoresis, on-line HPLC/ electrospray ionization MS and tandem MS. The major glycoconjugate was iden tified as protoporphyrin-1-O-acyl beta-xyloside with a smaller amount of pr otoporphyrin-1-O-acyl beta-glucoside also detected. In the Harderian glands studied, 50-70% of the porphyrins present were in the form of protoporphyr in glycoconjugates. This is the first reported occurrence of glycoconjugate s of porphyrins in Nature and suggests that previous studies have wrongly i dentified the major porphyrin in the Harderian gland as the unconjugated pr otoporphyrin.