Phosphorylation of yeast protein: Reduction of ribonucleic acid and isolation of yeast protein concentrate

Yeast nucleoproteins were chemically phosphorylated with phosphorus oxychloride (POCL(3)). Studies using (31)P nuclear magnetic resonance (NMR) spectroscopy, stability to pH and lysine estimation all indicated that the epsilon-amino group of lysine was the principal functional group phosphorylated. Phosphorylation of ca. 30% of the lysine residues resulted in removal of more than 85% of contaminant ribonucleic acid from protein precipitated at pH 4.2. Phosphorylation did not alter the amino acid composition of yeast proteins and was reversible under acidic conditions. Based on the data, a method for the preparation of phosphorylated yeast protein with low levels of nucleic acid is proposed.