Plant Ureases Research Articles

Is nickel a universal component of plant ureases?

A simple assay for ureolytic activity in intact callus was devised to screen rice, tobacco and soybean for the role of nickel in urease synthesis. When callus is grown with citrate (10 mM) urease levels are reduced approx. 5-fold (tobacco), 10-fold (rice) and 28-fold (soybean). It appears that citrate is depressing urease synthesis by chelating trace nickel in the medium thus making it less available to the callus cells: a 10 −2 mM Ni 2+ addition to citrate-containing growth medium stimulates urease levels approx. 11-, 8- and 17-fold respectively in tobacco, rice and soybean cultures. The antagonistic effects of citrate and nickel on callus urease levels are not correlated with effects on urea uptake or on callus growth. However, when urea is nitrogen source Ni 2+ consistently stimulates growth. In light of the conclusions of Dixon et al. [1], viz. that nickel is an act site component of jack bean urease, the observed stimulation of urease synthesis in soybean, tobacco and rice callus by nickel strongly suggests that this metal is a component of their ureases as well.

Urease from the lugworm, Arenicola cristata.

Urease from animal tissues is often considered to be of microbial rather than animal origin. A determination of key properties of urease isolated from an animal tissue should permit an assessment of the origin of the enzyme. Lugworm (A. cristata) gut urease was purified seventy fold from tissue homogenates by chromatography on DEAE-cellulose and Sephadex G-150. The apparent molecular weight by gel-filtration was 200,000. The Km for urea declined from about 3.5 mM at pH 6 to 0.38 mM at pH 7 then decreased with increasing pH to 0.2 mM at pH 9 in Tris-phosphate buffer. The Vmax was constant between pH 6 and 8 then declined above pH 8. N-ethylmaleimide, AgNO3 but not iodoacetamide inhibited enzyme activity. Acetohydroxamate, hydroxyurea, and hydroxylamine inhibited in the manner similar to the inhibition seen with ureases from other sources. The characteristic properties of A. cristata gut urease—low Km, pattern of variation of Km with pH, molecular weight, and sensitivity to inhibitors—distinguish this urease from urease in bacteria, plants, land snails and cestodes.

Antimicrobial activity of hydroxamic acids.

o-, m- and p-alkyloxybenzohydroxamic acids were synthesized and subjected to the examination for antibacterial and antifungal activity. All the hydroxamic acids tested were almost ineffective for pathogens examined of Enterobacteriaceae, but some of alkyloxybenzo- and fatty acyl-hydroxamic acid were found to be as highly effective for pathogenic fungi as butyl p-hydroxybenzoate being used as a comparison. The increase of carbon number of p-alkyloxybenzo- and fatty acyl-hydroxamic acid led to the increase in their antifungal activity, reached to the maximum at C6 in alkyloxy moiety and C10 in fatty acyl derivatives, and then the gradual decrease in both series. Considering the inhibitory power of hydroxamic acid on plant and bacterial urease, we discussed the possible correlation between antimicrobial activity and inhibitory powers on urease activity of the compounds.

In vitro and in vivo Responses of Ruminants to Ureolytic Inhibition

Nonprotein nitrogen compounds such as urea could be utilized more fficiently by ruminants if the rate of urea hydrolysis in the reticulorumen could be controlled. Suppression of the rate of bacterial hydrolysis would allow greater protein synthesis. Various methods that have been used to suppress entymatic action include physical encapsulation (Johnson et al., 1962), gelatinization (Bartley et al., 1968), enzyme inhibition by inorganic and organic compounds (Prescott, 1953; Johnson et al., 1962; Harbers et vl., 1962) and enzyme immunization (Harbers et al., 1965). Compounds that inhibit plant ureases are many (Shaw, 1953; Varner, 1960), however their effects on bacteria are variable as demonstrated with intact and ruptured cells of pure cultures (Lattimer et 41., 1961). Ureolytic inhibitors are effective in various monogastric species (Dintzis and Hastings, 1953; Visek, 1959) but less in ruminants (Johnson et v1., 1962) . We selected several inhibitors and studied their efficacy for ruminants using an in vitro artificial rumen system, in vivo reticulorumen ammonia concentrations, nitrogen retention and nutrient digestibility.

The inducible formation of urease in rice plants

Abstract Enzyme induction has been extensively investigated in bacteria. Recently the mechanism of enzyme induction has been made clear by the advances of research in molecular biology (1,2). Comparable studies with higher plants have received lens attention because of the relatively love rate of induction and there have been few reports about enzyme induction in higher plants (3–11).