Ureases display biological effects independent of enzymatic activity: Is there a connection to diseases caused by urease-producing bacteria?

Ureases are enzymes from plants, fungi and bacteria that catalyze the hydrolysis of urea to form ammonia and carbon dioxide. While fungal and plant ureases are homo-oligomers of 90-kDa subunits, bacterial ureases are multimers of two or three subunit complexes. We showed that some isoforms of jack bean urease, canatoxin and the classical urease, bind to glycoconjugates and induce platelet aggregation. Canatoxin also promotes release of histamine from mast cells, insulin from pancreatic cells and neurotransmitters from brain synaptosomes. In vivo it induces rat paw edema and neutrophil chemotaxis. These effects are independent of ureolytic activity and require activation of eicosanoid metabolism and calcium channels. Helicobacter pylori, a Gram-negative bacterium that colonizes the human stomach mucosa, causes gastric ulcers and cancer by a mechanism that is not understood. H. pylori produces factors that damage gastric epithelial cells, such as the vacuolating cytotoxin VacA, the cytotoxin-associated protein CagA, and a urease (up to 10 percent of bacterial protein) that neutralizes the acidic medium permitting its survival in the stomach. H. pylori whole cells or extracts of its water-soluble proteins promote inflammation, activate neutrophils and induce the release of cytokines. In this paper we review data from the literature suggesting that H. pylori urease displays many of the biological activities observed for jack bean ureases and show that bacterial ureases have a secretagogue effect modulated by eicosanoid metabolites through lipoxygenase pathways. These findings could be relevant to the elucidation of the role of urease in the pathogenesis of the gastrointestinal disease caused by H. pylori.

Efecto de la extrusión sobre la actividad de factores antinutricionales y digestibilidad in vitro de proteínas y almidón en harinas de Canavalia ensiformis / Effect of extrusion on the activity of anti-nutritional factors and in vitro digestibility of protein and starch in flours of Canavalia ensiformis

The effect of the extrusion (155 degrees C, 20 per cent moisture, screw speed 75 rpm, feed speed 205 g min-1) on antinutritional factors of Canavalia ensiformis was studied. In vitro protein and starch digestibilities were assessed. The extrusion not affect protein content (23 per cent) in the flours, but significantly (P < 0.01) decrease moisture content. The protein digestibility values were improved from 57.5 to 89.5 per cent, these values were lower than casein (98.19 per cent). The digestibility of starch values were improved from 37.7 to 53 per cent. The protease inhibitors activities (trypsin and chymotrypsin) and alpha-amylase inhibitor activity were reduced by 95 per cent. The haemagglutinating activity was eliminated as result of the high temperature employed during the extrusion process. The canavanine content in the flours were not affect by the treatment of extrusion.