The Cleavage of Prolyl Peptides by Kidney Peptidases

Peptides of the X‐Pro‐Y type were found to be readily cleaved by crude swine kidney homo‐genates. Using Gly‐Pro‐Hyp as a substrate, a peptidase releasing glycine was isolated and partially purified from the microsomal fraction of the homogenate. The purification steps used included treatment of the kidney microsomes with n ‐butanol, and chromatography of the protein fraction thus released on DEAE‐cellulose as well as gel filtration on Sephadex G‐200. The increase in specific activity was approximately 250‐fold. The purified preparation consisted of two enzymatically active components exhibiting molecular weights of one million and two millions, respectively. There is evidence that these components are lipoproteins, i.e. membrane fragments of different size. The activity of the enzyme was optimal at pH 8 and was greatly increased in the presence of manganese ions and albumin. Since the peptidase required a prolyl residue in the second position of the substrate, the designation “X‐prolyl‐aminopeptidase” is suggested. Although the enzyme acted on substrates of different chain length, the reaction rates were greatest with peptides of the structure Gly‐Pro‐Y. Therefore, a role of X‐prolyl‐aminopeptidase in the degradation of collagen appears plausible.