Separation and characterization of two carnosine-splitting cytosolic dipeptidases from hog kidney (carnosinase and non-specific dipeptidase)

High performance anion-exchange chromatography was used to separate two carnosine-hydrolysing dipeptidases from hog kidney. Both enzymes (peaks I and II) were cytosolic and were activated and stabilized by Mn2+ and dithiothreitol. Peak I had a narrow specificity when assayed without added metal ions, but a broad specificity in the presence of Mn2+ or Co2+. Peak II was inactive unless both Mn2+ and dithiothreitol were present. Bestatin and leucine inhibited peak II, but not peak I. Peak I had a Km of 0.4 mM carnosine, a pI of 5.5 and a Mr of 57,000. Peak II had a Km of 5 mM carnosine, a pI of 5.0 and a Mr of 70,000. Hog and rat brain and liver carnosinase activity was completely inhibited by bestatin, indicating that these organs contained peak II, with little or no peak I enzyme. Hog kidney peak I contained the classical carnosinase of Hanson and Smith, who first described this enzyme. It also contained activity against homocarnosine ("homocarnosinase") and showed "manganese-independent carnosinase" activity. These three activities could not be separated using 8 different chromatographic procedures; it was concluded that they are attributable to one enzyme. It is recommended that the name carnosinase be retained for this enzyme and the names "homocarnosinase" and "manganese-independent carnosinase" be withdrawn. The properties of hog kidney peak II closely resembled those of human tissue carnosinase (also known as prolinase, a non-specific dipeptidase), mouse "manganese-dependent carnosinase" and a rat brain enzyme termed "beta-Ala-Arg hydrolase". Since these terms appear to represent closely related enzymes with broad specificity, the recommended name for each is "non-specific cytosolic dipeptidase".