Hydroxyproline distribution in the plasma of various mammals

We have investigated the presence of total, free, protein-bound and peptide-bound hydroxyproline (Hyp) in the plasma of different mammals viz., camel, bovine, sheep, human, rabbit and rat. Total Hyp was significantly highest in human followed by rabbit, rat, bovine, sheep and camel (P<0.001). Free Hyp was significantly highest in human followed by rabbit, rat, camel, bovine and sheep (P<0.001). However, the protein-bound Hyp content was significantly highest in rat followed by bovine, human, camel, rabbit and sheep (P<0.001). Peptide-bound Hyp was significantly highest in human plasma followed by sheep and rabbit (P<0.001). No peptide-bound Hyp was detected in the plasma of camel, bovine or rat. In the human plasma, peptide-bound Hyp constituted 60% of the total plasma Hyp, followed by protein-bound Hyp, which was 35% of the total, Hyp and free Hyp, which was 15% of the total plasma Hyp. In the sheep plasma peptide-bound Hyp constituted about 50% of total Hyp followed by protein-bound (40% of the total Hyp) and free Hyp, which formed 10% of total Hyp. In the rabbit plasma protein-bound Hyp constituted 50% of the total Hyp fraction, followed by peptide-bound and free, which constituted about 30 and 20%, respectively, of the total Hyp fraction of the plasma. Peptide-bound Hyp formed 92, 84 and 82% of the total plasma Hyp in rat, camel and bovine, respectively. Free Hyp constituted about 8% of the total plasma Hyp in rat and 18% of total Hyp in bovine and camel, respectively. The causes of the significant variations in different collagen structure and composition with respect to the different species examined are not known, however, these variations may results from differences in turn-over rate of Hyp in those species.