The isolation, purification, and properties of a ribonuclease (Mr 18 000) from human uremic serum, and its relation to the human urinary ribonuclease (Mr 33 000). II. Properties of the enzymes.

A low molecular weight ribonuclease (Mr 18 000) isolated and purified from human uremic serum was found to have similar properties to the high molecular weight ribonuclease (Mr 33 000) isolated from human urine. A detailed comparative study of both enzymes was undertaken to investigate the relationship between them. It is suggested that poly(C)-avid human ribonucleases have similar amino acid compositions but variable carbohydrate contents and that variations in the sugar content are responsible for variations in the molecular weight.