Determination of the primary and secondary structures of the dromedary (Camelus dromedarius) prolactin and comparison with prolactins from other species.

A non-glycosylated form of camel prolactin (camPRL), isolated from one-humped camel (Camelus dromedarius) pituitaries, was totally sequenced. A glycosylated form, separated by affinity chromatography on ConA-Sepharose, was partially sequenced. The comparison of the N-terminal amino acid sequences of the glycosylated and non-glycosylated forms showed that the only putative site of N-glycosylation (Asn-31) was indeed glycosylated. The far ultraviolet (UV) circular dichroism (CD) spectra of the two isohormones were identical, suggesting that the carbohydrate moiety had no effect on the global camPRL secondary structure. The far UV circular dichroism spectra of the two isohormones were analyzed in order to determine their relative proportions of periodic secondary structure, 60% of which was found to be in alpha-helix, as in prolactins of other species. The dromedary sequence was compared to those of other species and interpreted in term of evolutionary process. As already found for gonadotropins, the closest species to the dromedary was found to be the pig.