Phosphatases in the soil environment

Abstract

<p>Enzymes play a key role in nutrient cycling in the soil environment. In this work, four phosphatases of the soil environment were investigated. A study of the effect of metal ions and metal ion concentrations on inorganic pyrophosphatase activity in three NH(,4)OAc-leached soils showed that seven of the metal ions tested promoted activity. The average efficiency of these metal ions in promoting pyrophosphatase in decreasing order was: Ca('2+) > Mg('2+) > Ba('2+) = Co('2+) > Ni('2+) > Zn('2+) > Mn('2+). Sodium ions and K('+) did not affect pyrophosphatase activity and Cu('2+) and Fe('2+) decreased this activity. Optimum pyrophosphatase activity occurred at a Mg('2+):PPi or Ca('2+):PPi ratio of 1:1. Protection of pyrophosphatase in the NH(,4)OAc-leached soils against heat inactivation by Mg('2+) and Ca('2+) was also observed;The rates of hydrolysis of seven organic and two inorganic phosphorus compounds added to soils and incubated under aerobic or waterlogged conditions showed that monomethyl phosphate, (beta)-glycerophosphate, and (alpha)-D-glucose-1-phosphate were hydrolyzed at similar rates in the three soils used. Disubstituted organic P compounds (e.g., diphenyl phosphate and bis-p-nitrophenyl phosphate) were hydrolyzed at slower rates than monosubstituted organic P compounds (e.g., phenyl phosphate and p-nitrophenyl phosphate). Of the two inorganic P compounds studied, ammonium tetrametaphosphimate did not hydrolyze in soils, and the rates of hydrolysis of phosphonitrilic hexamide were very small (6-13% hydrolyzed in 7 days) compared with those of the organic phosphates (30-100%). The rates of hydrolysis of the mono- and disubstituted organic P compounds were related to the levels of acid phosphatase and phosphodiesterase, respectively, in the three soils studied;Comparisons of pH optima and kinetic parameters (K(,m), V(,max), and E(,a)) for acid and alkaline phosphatases, phosphodiesterase, and pyrophosphatase among plant materials, manures, sewage sludges, and soils were made. A 120-day incubation experiment in which soils were treated with corn plant material, hog manure, or sewage sludge showed that these materials did not permanently increase acid phosphatase and pyrophosphatase activity of soils. Addition of sodium azide, however, decreased the activity of these enzymes significantly (P < 0.05) after 120 days of incubation;Acid phosphatase and inorganic pyrophosphatase from sterile corn roots were inhibited by clay minerals. The inhibition of these enzymes by montmorillonite and illite followed partial noncompetitive kinetics while the inhibition by kaolinite followed partial competitive kinetics. The clay minerals did not release any inhibitory compounds, but their inhibition of acid phosphatase and pyrophosphatase seem due to the adsorption of these enzymes by the clay minerals. The adsorption of acid phosphatase and pyrophosphatase by clay minerals was considered ionic in nature.</p>