Proprietes des activites proteolytiques extraites des sols frais

Abstract

Properties of proteolytic active extracts from soils: NAFS Extract (neutral sterile and lyophilized extracts of fresh soil) and EFS Extract (NAFS Extract treated with salmine and SP Sephadex C25 to remove humic matter) had proteolytic activity (substrate casein) associated with o- and p- diphenol oxidases. The proteolytic activity of NAFS Extract was positively correlated with soil organic matter content and negatively correlated with soil clay content. The proteolytic activity seemed to be associated with the growth of proteolytic bacteria but not with their number. Proteolytic activity of EFS Extract was optimal at pH 8·5 and at 50°C. Between 14°C and 37°C, the E act. was 5·8 Kcal mole −1 °C −1. By varying the casein concentration, we obtained that V max = 1 UPK (Kaken) mg C −1 EFS and K m = 2·2% (w/v). The proteolytic activity was insensitive to iodoacetamide (10mM) p- chloromercuribenzoate (10μM) and EDTA (50 mM), but highly sensitive to diisopropylphosphofluoridate (100 μM). These results suggested that the proteolytic activity associated with the EFS Extract was a serine protease of the alkaline type. The stability of diphenol oxydases and serine protease in EFS Extract was discussed. In the presence of lysozyme and pronase, the activity of diphenol oxidase was destroyed. Pronase alone had only a little effect on this activity. This suggests that polysaccharides associated with EFS and NAFS extracts play a role in stabilizing the “humoenzymes” system in soil.