Streptomyces griseus aminopeptidase is a calcium‐activated zinc metalloprotein

Abstract

A heat‐stable aminopeptidase with an N‐terminal Ala‐Pro‐Asp‐Ile‐Pro‐Leu sequence has been purified from Streptomyces griseus by heat treatment followed by gel‐exclusion and anion‐exchange chromatographic procedures. The enzyme is a monomeric zinc metalloenzyme showing an apparent molecular mass of 33 kDa by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and 21 kDa by gel filtration on Superose 12. Calcium ions bind to the enzyme, p K Ca 4.5, and activate it about sixfold when the substrate is leucine‐4‐nitroanilide (0.4 mM in 50 mM Tris/HCl pH 8.0, 25°C). Binding of Ca 2+ also contributes to the thermal stability of the protein. This aminopeptidase may be useful for two‐stage assays of bacterial and mammalian metalloendopeptidases; it may also serve in studies of proteolytic enzyme activation by calcium ions.