Protein 1: its purification and application in clinical medicine

Protein 1 (P1) is a low-molecular-weight protein recently isolated from the urine of patients with chronic renal failure. Its molecular weight is 14 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis and pI 4.7 on isoelectric focusing. We purified this protein, characterized its physicochemical properties, and analyzed its amino acid sequences to show that it is probably identical to human lung Clara cell 10 kDa protein. Its monoclonal antibody was prepared, and a reliable enzyme-linked immunosorbent assay employing the sandwich method was developed and used to investigate distribution and variation in concentration of P1 in various body fluids under an array of physiologic and pathologic conditions. Clinical studies indicated that, as is the case with other proteins of low molecular weight, the main catabolic site of P1 of plasma origin is the kidney: P1 is filtered by the renal glomeruli and reabsorbed by the renal tubules. Unabsorbed P1 is thus excreted into the urine. This protein is also synthesized in the genital tissues of males, however, from which it is also excreted into the urine. Clinical data obtained in our study of this protein is summarized here, and an attempt is made to determine the potential value of this protein in laboratory medicine.