Characterization of a protease component extracted from a paddy soil under monoculture of rice

Abstract

Most of the organisms which are non-nitrogen fixers, must decompose protein to low molecular nitrogenous compounds to be able to assimilate nitrogen. Proteins are supplied to soil from various dead organisms. About 0.5 kg kg⁻¹ of dry weight of bacterial cells consists of protein (Luria 1960). Proteases are enzymes which hydrolyze proteins to amino acids. In soil, proteases are released by the microbial community (Ladd and Paul 1973; Hayano 1993; Watanabe and Hayano 1993) and the hydrolysis of protein, like ammonification and nitrification, is important in the nitrogen cycle which plays an essential role in soil fertility. Previously, a protease extracted from the top soil of an Andosol was found to correspond to metalloendopeptidase (EC 3.4.24) with a molecular weight and isoelectric point of 47 kDa and 4.9, respectively (Hayano et al. 1987). In the present study, we characterized the properties of a protease extracted from the non-rhizosphere soil of a flooded paddy field under monoculture of rice.

Key Words:

• metalloprotease
• nitrogen transformation
• protease
• soil enzyme
• soil extract