Characterization of human tissue carnosinase.
Human tissue carnosinase (EC 3.4.13.3) had optimum activity at pH9.5 and was a cysteine peptidase, being activated by dithiothreitol and inhibited by p-hydroxymercuribenzoate. By optimizing assay conditions, the activity per g of tissue was increased 10-fold compared with values in the literature. The enzyme was present in every human tissue assayed and was entirely different from serum carnosinase. Highly purified tissue carnosinase had a broader specificity than hog kidney carnosinase. Although tissue carnosinase was very strongly inhibited by bestatin, it did not hydrolyse tripeptides, and thus appears to be a dipeptidase rather than an aminopeptidase. It had a relative molecular mass of 90 000, an isoelectric point of 5.6, and a Km value of 10 mM-carnosine. Two forms of kidney and brain carnosinase were separated by high-resolution anion-exchange chromatography, although only one form was detected by various electrophoretic methods. Homocarnosinase and Mn2+-independent carnosinase were not detected in human tissues, although these enzymes are present in rat and hog kidney.
D002413:Cations, Divalent / Q000494:pharmacology; D004150:Dipeptidases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D004586:Electrophoresis; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D013379:Substrate Specificity; D014018:Tissue Distribution
D002413:Cations, Divalent; D004150:Dipeptidases; C019673:aminoacyl-histidine dipeptidase; D004229:Dithiothreitol