Zur verwendung von l-leucin-β-naphthylamid als spezifisches substrat für bestimmungen von leucinaminopeptidase

Abstract

Serum of normal persons and especially of pregnant women splits l-leucine-β-naphthylamide (LN) better than L-leucinamide (LA). In human placenta and rat kidney, but especially in rat liver and bovine lens, LA is split much better than LN. The splitting of LN in bovine lens, rat liver and rat kidney cytoplasm can be distinctly activated by Mn ++, but in placenta and serum it is inhibited by Mn ++, whereas the splitting of LA is activated by Mn ++ in all these enzyme sources (except in serum). The particle fractions of rat livers and kidneys contain at least one more enzyme which distinguishes itself from the cytoplasmic LAP by a better LN splitting and a different influence of the metal ions. Perfused, autolysing rat livers lose a particularly great amount of LAP, whereas the enzyme more readily splitting LN is retained by the cells for more than 3 h at 37°. According to these results, a correlation between the splitting of LN and the LAP activity cannot be established without limitation. Studies permitting to draw conclusions from the LN splitting with reference to the LAP activity should be preceded by a comparison between the splitting of LA and LN. For exact quantitative determinations of LAP a paper chromatographical procedure is recommended to determine leucine, using the typical LAP substrate LA.