Physicochemical properties of a proline-rich polypeptide (PRP) from ovine colostrum

Properties of a proline-rich polypeptide (PRP) accompanying ovine colostral IgG2 are described. PRP is soluble at 4 degrees C but reversibly precipitates by warming to room temperature. Maximal precipitation is observed at pH = 4.6, temp. 48 degrees C, and ionic strength higher than 0.6. There is a linear dependence of precipitation on concentration of PRP. Molecular weight of PRP is 38,000 daltons. It is not changed in the presence of 6 M guanidine hydrochloride, SH-compounds, and in the presence or absence of metal ions. PRP is built of one polypeptide chain. No difference in proteolysis of IgG2 by pepsin, papain and trypsin in the absence or presence of PRP was found.