Canatoxin is a toxic protein from Canavalia ensiformis seeds, lethal to mice (LD50 = 2mg/kg) and insects. Further characterization of canatoxin showed that its main native form (184kDa) is a non-covalently linked dimer of a 95kDa polypeptide containing zinc and nickel. Partial sequencing of internal peptides indicated homology with urease (EC 184.108.40.206) from the same seed. Canatoxin has approx. 30% of urease's activity for urea, and Km of 2–7mM. The proteins differ in their affinities for metal ions and were separated by affinity chromatography on a Zn2+ matrix. Similar to canatoxin, urease activates blood platelets and interacts with glycoconjugates. In contrast with canatoxin, no lethality was seen in mice injected with urease (10mg/kg). Pretreatment with p-hydroxymercuribenzoate irreversibly abolished the ureolytic activity of both proteins. On the other hand, p-hydroxymercuribenzoate-treated canatoxin was still lethal to mice, and both treated proteins were fully active in promoting platelet aggregation and binding to glycoconjugates. Taken together, our data indicate that canatoxin is a variant form of urease. Moreover, we show for the first time that these proteins display several biological effects that are unrelated to their enzymic activity for urea.
Canatoxin, a toxic protein from jack beans (Canavalia ensiformis), is a variant form of urease (EC 220.127.116.11): biological effects of urease independent of its ureolytic activity
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Cristian FOLLMER, Grace B. S. BARCELLOS, Russolina B. ZINGALI, Olga L. T. MACHADO, Elias W. ALVES, Christina BARJA-FIDALGO, Jorge A. GUIMARÃES, Célia R. CARLINI; Canatoxin, a toxic protein from jack beans (Canavalia ensiformis), is a variant form of urease (EC 18.104.22.168): biological effects of urease independent of its ureolytic activity. Biochem J 15 November 2001; 360 (1): 217–224. doi: https://doi.org/10.1042/bj3600217
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