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Crystalline Ribonuclease from Bovine Milk

Eastern Regional Research Laboratory,¹ Philadelphia, Pennsylvania

ABSTRACT

Bingham and Zittle (1) isolated ribonuclease from bovine milk using IRC-50 resin and found it to be identical to pancreatic ribonuclease A. In separating the red protein and lactoperoxidase from milk with DEAE cellulose and phosphocellulose adsorbents (2), ribonuclease was obtained as a by-product. Since milk is a good source of ribonuclease, this report will deal with another method for its isolation. Also, starting with a small amount of material, milk ribonuclease was crystallized and its disc electrophoretic properties determined.

The fractionation of milk from a single cow and the chromatographic procedures for isolating ribonuclease followed the methods described for the isolation of the iron-binding proteins (2). The two fractions eluted from the phosphocellulose column with 0.1 n phosphate-0.05 M NaCl, pH 6.5, and 0.1 M phosphate-0.1 M NaCl, pH 6.9, were greenish in color and contained lactoperoxidase and ribonuclease. The proteins were recovered from these two fractions and resolved on a Sephadex G-200 column 2 by 70 cm previously equilibrated with 0.1 M phosphate, pH 7.0, at 3 degrees.

¹ Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.