Characterization of β‐d‐glucosidase extracted from soil fractions

Abstract

Summary One way to study the state in which stabilized extracellular enzymes persist and are active in the soil is by extraction from the soil, with subsequent fractionation of enzyme–organomineral complexes and characterization of such complexes. In order to investigate the location and characteristics of soil β‐glucosidase, three soil fractions were obtained both from real (undisturbed) soil aggregates and from structural (dispersed in water and physically disrupted) aggregates using two different granulometric procedures. The β‐glucosidase activity of the fraction was then assayed. When the aggregates were dispersed, more than 73% of activity was in the soil microaggregates with diameters of less than 50 μm (SF50). These aggregates were associated with strongly humified organic matter. Solutions of diluted pyrophosphate at neutral pH liberated active β‐glucosidase from all fractions, although the efficacy of extraction varied according to the type of fraction. The SF50 fraction and aggregates of 2000–100 μm obtained by sieving (SF2000) showed the greatest β‐glucosidase activity (34.5 and 36.0%, respectively). Micro‐ and ultrafiltration of SF50 extracts increased the total β‐glucosidase activity, whereas these procedures, applied to the RF2000 fraction, decreased it. Humus–β‐glucosidase complexes in the SF50 fraction, between 0.45 μm and 105 nominal molecular weight limit ( nmwl) (SF50II) and < 105nmwl (SF50III) showed an optimum pH at 5.4, and in the SF50I fraction (> 0.45 μm) the optimum was 4.0. The stability of β‐glucosidase 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 and maximum velocity was observed in all but one of the β‐glucosidase complexes extracted and partially purified from the SF50 aggregates.

Occurrence and Fate of the Phytotoxin Juglone in Alley Soils under Black Walnut Trees

“…Juglone from black walnut trees to soil is thought to exist primarily as α‐hydrojuglone glucoside, which is relatively benign, but can be rapidly oxidized to juglone (Daglish, 1950; Willis, 2000). Release of juglone from the parent glucoside in plants is considered to be a two‐step process with β‐glucosidase, a common soil enzyme (Alef and Nannipieri, 1995; Busto and Perez‐Mateos, 2000), catalyzing the hydrolysis to hydrojuglone (Duroux et al, 1998) followed by the fast chemical oxidation to the quinonoidal compound juglone (Duroux et al, 1998; Müller and Leistner, 1976). Potential juglone abundance estimated in walnut leaves, hulls, and roots ranges from less than 0.1% dry wt.…”

Adsorption, immobilization, and activity of β-glucosidase on different soil colloids

“…However, soil enzymatic reactions occur in a heterogeneous rather than homogeneous environment [8]. A certain proportion of free enzymes may undergo stabilization through adsorption on soil minerals or through incorporation into humic material [9,10] and, despite affecting their catalytic potential [11], may enable enzyme activity to remain active for long periods in soil. The adsorption and immobilization process can affect the conformational structure of enzymes, and, in turn, enzyme activity and kinetic changes may result due to the interaction between enzyme and substrate at solid-solution interfaces [12,13].…”

Thermostability of Selected Enzymes in Organic Wastes and in their Humic Extract

“…Synthesis of o-DPO by microorganisms is induced by HSD Honestly significant differences, which are obtained using the multiple range test of Tukey different substrates, including anilines, aromatic compounds, or lignin preparations [15], and investigations have focused on the role of this enzyme in lignin degradation during composting process [16,17]. These compounds, in a second step, are polymerized and integrated in the humus molecule [12].…”