Characterization of beta-D-glucosidase extracted from soil fractions

One way to study the state in which stabilized extracellular enzymes persis t and are active in the soil is by extraction from the soil, with subsequen t fractionation of enzyme-organomineral complexes and characterization of s uch complexes. In order to investigate the location and characteristics of soil beta-glucosidase, three soil fractions were obtained both from real (u ndisturbed) soil aggregates and from structural (dispersed in water and phy sically disrupted) aggregates using two different granulometric procedures. The beta-glucosidase activity of the fraction was then assayed. When the a ggregates were dispersed, more than 73% of activity was in the soil microag gregates with diameters of less than 50 mu m (SF50). These aggregates were associated with strongly humified organic matter. Solutions of diluted pyro phosphate at neutral pH liberated active beta-glucosidase from all fraction s, although the efficacy of extraction varied according to the type of frac tion. The SF50 fraction and aggregates of 2000-100 mu m obtained by sieving (SF2000) showed the greatest beta-glucosidase activity (34.5 and 36.0%, re spectively). Micro- and ultrafiltration of SF50 extracts increased the tota l beta-glucosidase activity, whereas these procedures, applied to the RF200 0 fraction, decreased it. Humus-beta-glucosidase complexes in the SF50 frac tion, between 0.45 mu m and 10(5) nominal molecular weight limit (nmwl) (SF 50II) and < 10(5) nmwl (SF50III) showed an optimum pH at 5.4, and in the SF 50I fraction (> 0.45 mu m) the optimum was 4.0. The stability of beta-gluco sidase in the aggregates of the smallest size SF50II and SF50III decreased at acid pHs. The presence of two enzymes (or two forms of the same enzyme) catalysing the same reaction with different values of Michaelis constant an d maximum velocity was observed in all but one of the beta-glucosidase comp lexes extracted and partially purified from the SF50 aggregates.