Towards an understanding of biological role of colostrinin peptides.

The aim of this study was to elucidate the structure and possible function of colostrinin, also known as a proline rich polypeptide (PRP). The molecular weight of colostrinin was originally determined by gel filtration to be 17,200 daltons. In the presence of guanidinum chloride, however, the molecular weight was found to be about 6,000 daltons. Further studies utilizing high-performance liquid chromatography (HPLC) and mass spectroscopy revealed that colostrinin is a complex consisting of many low molecular-weight polypeptides. A total of 32 peptides were isolated from the original colostrinin preparation by HPLC and subjected to the N-terminal sequence analysis. The results of sequence analysis revealed significant homology of the peptides to three protein precursors: annexin, beta-casein, and a hypothetical beta-casein homolog. In addition, the sequence of several peptides showed no significant homology to any specific protein in the current GenBank database. The synthetic peptides of various lengths representing the N-terminal sequence of the colostrinin peptides were made to study some biological effects. Here we report that colostrinin and some of its component peptides are potent inducers of leukocyte proliferation and of certain cytokines. Also, a series of monospecific antibodies were produced in rabbits against the synthetic peptides. The antibodies were used to study the kinetic of antigen reduction in colostrum and mature milk following lambing. A threefold decrease was common for most antigens studied over the period of 72 h. Based on the results of these studies we postulate that colostrinin represents a diverse group of peptides produced in the mammary gland of mammals for the development of the optimal physiologic responses in offspring. Also, it is hoped that the beneficial use of colostrinin in Alzheimer's Disease (AD), recently reported elsewhere, will revive interest in its clinical application for treatment and/or prophylaxis of many age-related disorders.