Soybean proteins were enzymatically phosphorylated with the catalytic subunit of cAMP-dependent protein kinase isolated from bovine cardiac muscle. Both of the major storage proteins, /3-conglycinin and glycinin, were phosphorylated. Heat denaturation of the soy proteins increased the amount of r-32P incorporation. Soy isolates incorporated up to 0.88 mol of phosphate/mol of /3-conglycinin and over 1.0 mol of phosphate/mol of glycinin. Enzymatic phosphorylation could provide a means of increasing the solubility of soy proteins at mildly acidic pH and thus extend the availability of soy proteins for use in the food system.

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