Degradation of prolylleucylglycinamide (MIF) by mouse brain

Abstract

Prolylleucylglycinamide (MIF) at 1.0 mM concentration and pH 7.0 was hydrolyzed by mouse brain homogenate at a rate of 140 nmol/mg protein/hr. Nearly all of this activity can be accounted for by the action of two enzymes, both of which cleave Pro and Leu sequentially from the N-terminus of MIF. At pH 7.0 the predominant enzyme is arylamidase, inhibited by puromycin (1mM) and Mn²⁺ (2.5 mM). At pH 8.5, in the presence of Mn²⁺, a second enzyme with a higher potential activity (570 nmol/mg protein/hr) was observed. While the arylamidase is primarily localized in the cytosol, the Mn²⁺-stimulated enzyme is equally divided between soluble and particulate fractions. Because of its ability to cleave leucinamide, its high pH optimum, and its Mn²⁺ dependence, it can be classified as a leucine aminopeptidase (LAP). In its substrate specifically and its preference for Mn²⁺ over Mg²⁺ it resembles the LAP from connective tissue more than that from other sources.