Engineering topics
Publications and source records attributed to Mclaren, A. D..
Sensitive tests for the detection of extracellular enzyme activity in Martian soil was investigated using simulated Martian soil. Enzyme action at solid-liquid water interfaces and at low humidity were studied, and a kinetic scheme was devised and tested based on the growth of microorganisms and the oxidation of ammonium nitrite.
An exploration was made of enzyme activities in soil, including abundance, persistence and localization of these activities. An attempt was made to develop procedures for the detection and assaying of enzymes in soils suitable for presumptive tests for life in planetary soils. A suitable extraction procedure for soil enzymes was developed and measurements were made of activities in extracts in order to study how urease is complexed in soil organic matter. Mathematical models were developed, based on enzyme action and microbial growth in soil, for rates of oxidation of nitrogen as nitrogen compounds are moved downward in soil by water flow. These biogeochemical models should be applicable to any percolating system, with suitable modification for special features, such as oxygen concetrations, and types of hydrodynamic flow.
Urease activity in soil is persistent for long periods under low water, low temperature, and sterile regimes, and it was suggested that some form of enzyme-protective mechanism exists in soil. Dublin soil was extracted by sonication in water followed by adding a mixture of salts. Urease activity is associated with the organo-mineral complex thus obtained and is resistant to the activities of proteolytic enzymes. Clay free soil organic matter prepared subsequently by filtration also exhibits urease activity which is resistant to proteolysis. Models consisting of enzymes with bentonite and lignin were found to mimic this resistance to proteolysis. A model system is presented which suggests both the origin and location of soil ureases and a reason for their persistence in nature.
Description of an extraction from a Dublin clay loam soil of a colloidal organic matter complex that is urease active and, by X-ray analysis, free of clays. Urease activity in the clay-free precipitates, as in the soil, was not destroyed by the activity of an added proteolytic enzyme, pronase. This is attributed to the circumstance that native soil urease resides in organic colloidal particles with pores large enough for water, urea, ammonia, and carbon dioxide to pass freely, but nevertheless small enough to exclude pronase.
Urea hydrolysis reaction rates by urease at low water activity, noting use for Mars surface bioassay
Streptomyces sp chitinase purification and properties by column chromatography, noting calcium component
Nitrification reactions in soil with constant ammonium solution entry rate and nitrifying organisms, considering ion concentrations as functions of time and distance
Consecutive reaction equations for idealized soil column solved for nitrifying metabolite concentrations as functions of time and depth
Urease activity determined by using C 14 urea in stored, preserved /Permafrost/ and irradiated soils
Enzyme reaction rates of dry urea and urease in controlled atmospheric water vapor pressures, determining water vapor adsorption isotherms
Microbial numbers relation to phosphatase activity in soil, discussing seasonal variation, sterilization by irradiation and moisture content
Fluorimetric technique for phosphatase activity in soil based on beta-naphthol release from sodium- beta-naphthylphosphate