Uropepsinogen in human urine: its protein nature, activation and enzymatic properties of activated enzyme

Uropepsinogen (UPG) in human urine was highly purified by chromatography on columns of DEAE-lignocellulose, elastin-celite, etc. The purified UPG was composed of two electrophoretically distinguishable components (UPG I and UPG II), and they were isolated in the pure state, respectively. UPG I and UPG II were the same in molecular weight (3.9 X 10(4)) and in N-terminal (leucine) and C-terminal (alanine) amino acid residues. Also, they were quite similar in amino acid composition. They were activated to uropepsin (UP I and UP II, molecular weight, 3.3 X 10(4), respectively), but the activated enzymes were the same in the various properties examined, suggesting that the difference between UPG I and UPG II is due to only a minor change in the peptide segment, perhaps by deamidation. The activation of UPG I and UPG II occurred at acid pHs, the best pH being at 2.0. Both the proenzymes previously incubated with pepstatin at pH 6.8, however, were not activated even in the following incubation at acid sides. The results obtained are discussed in regard to the origin of the proenzyme and its properties before and after activation.