Leucine Aminopeptidase

Leucine aminopeptidase (LAP) is an exopeptidase hydrolyzing the peptide bond adjacent to a free amino group. It has been reviewed by Delange and Smith (1971). LAP is extensively used in the sequence analysis of proteins and peptides. See Rover and Andrews (1973).

Characteristics of Leucine Aminopeptidase from Hog Kidney:

Molecular weight: 255,000 ± 5,000 (Melius et al. 1970); 326,000 (Kretschmer et al. 1965).

Composition: LAP consists of four subunits each having one atom of zinc. (Himmelhoch 1969).

Optimum pH: Approximately 9.1 for the Mn²⁺ activated enzyme (Smith and Spackman 1955).

Inhibitors: Cd²⁺, Cu²⁺, Hg²⁺, Pb²⁺, EDTA, alcohols, p-chloromercuribenzoate, and bestatin. Himmelhoch (1969) reports very rapid inactivation by orthophenanthroline, bipyridyl, cupferron, sodium diethyldithiocarbamide, sodium sulfide and sodium cyanide. See also Melius and McAuliffe (1975), Birch et al. (1972) and Melius et al. (1972).

Activators: Mg²⁺ or Mn²⁺ , 3-4 mM, are essential for activity (Bryce and Rabin 1964).

Specificity: The enzyme liberates amino acids from the N-terminal end of a number of proteins and polypeptides. It is called leucine aminopeptidase because it reacts most rapidly with leucine compounds. Many aliphatic amides are also hydrolyzed as well as thiolesters (Metrione 1972). See also Jost et al. (1974).

Stability: The enzyme is stable in solution for several days when maintained in the presence of Mg²⁺, pH 8.0-8.5, at 4°C. As a suspension in ammonium sulfate containing Mg²⁺, pH 8.0-8.5, the enzyme is stable for months refrigerated.