A study of the activity of a serum enzyme or enzymes capable of hydrolyzing l-leucine-β-naphthylamide has shown that this enzyme (LNH) is not markedly elevated in patients with carcinoma of the breast and that the degree of progression of the disease bears no consistent relationship to the serum enzyme level. The enzyme was partially purified by chromatography on DEAE columns. The preparations so isolated were incapable of hydrolyzing other peptides at a significant rate. These data, along with variations in the ratios of leucine amino peptidase and LNH, indicate a degree of specificity for the enzyme which differentiates it from classical leucine amino peptidases.

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Supported by a grant from the American Cancer Society.

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