Leucine aminopeptidase from etiolated barley seedlings: characterization and partial purification of isoforms

Leucine aminopeptidase (LAP) is a terminal enzyme catalyzing a cycle of protein turnover. The normal properties of LAP from plants show a hexameric structure, thermostability over 60 °C and optimum pH of approximately 9.5. We isolated three types of LAP from etiolated barley seedlings, which were designated as LAP 1, LAP 2 and LAP 3. All of the subunit compositions were 57 kDa of monomeric structure. The thermostability of LAP 1, LAP 2 and LAP 3 was indicated by the enzymes having 50% of maximum activities, 51, 54 and 56 °C, respectively. The optimum pH was 7.0 for LAP 1 and LAP 2, and 8.0 for LAP 3. LAP activity was found almost equally in leaf tissue, coleoptile and roots from etiolated and green seedlings. All LAPs were sensitive to p-chloromercuribenzoic acid. LAPs from barley seedlings provide novel properties compared to LAPs from other plant species.