Characterization of dehydropeptidase I in the rat lung

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Abstract
The activity of dehydropeptidase I in rat tissues decreases in the order of lung > kidney > liver‐spleen > other tissues, while aminopeptidase activity is high in the kidney, and lower in the lung than in other tissues. Dehydropeptidase I was solubilized from the membrane fraction of rat lung by treatment with papain and purified by DEAE‐cellulose column chromatography, affinity chromatography on concanavalin‐A‐Sepharose and high‐performance liquid chromatography gel filtration. The purified preparation was found to be homogeneous on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The relative molecular mass was estimated to be 150000 by gel filtration, comprising a homodimer of two 80000‐Mr subunits. The enzyme activity was inhibited by cilastatin, o‐phenanthroline and ATP. This enzyme catalyzed the hydrolysis of S(substituent)‐l‐cysteinyl‐glycine adducts such as l‐cystinyl‐bis(glycine) and N‐ethylmaleimide‐S‐l‐cysteinyl‐glycine, as well as the conversion of leukotriene D4 to E4. Furthermore it catalyzed a hydrolytic splitting of l‐Leu‐l‐Leu, but not S‐benzyl‐l‐cysteine p‐nitroanilide, which is a good substrate for aminopeptidase. Our enzyme preparation was immunologically identical to the rat renal dehydropeptidase I. The physiological significance of the pulmonary dehydropeptidase I on the metabolism of glutathione and its adducts is discussed.