Purine requirements for the expression of Cape buffalo serum trypanocidal activity

Cape buffalo serum contains xanthine oxidase which generates trypanocidal H 2O2 during the catabolism of hypoxanthine and xanthine. The present studies show that xanthine oxidase-dependent trypanocidal activity in Cape buffalo serum was also elicited by purine nucleotides, nucleosides, and bases even though xanthine oxidase did not catabolize those purines. The paradox was explained in part, by the presence in serum of purine nucleoside phosphoryl ase and adenosine deaminase, that, together with xanthine oxidase, cataboli zed adenosine, inosine, hypoxanthine, and xanthine to uric acid yielding tr ypanocidal H2O2. In addition: purine catabolism by trypanosomes provided su bstrates for serum xanthine oxidase and was implicated in the triggering of xanthine oxidase-dependent trypanocidal activity by purines that were not directly catabolized to uric acid in Cape buffalo serum, namely guanosine, guanine, adenine monophosphate, guanosine diphosphate, adenosine 3':5-cycli c monophosphate, and 1-methylinosine. The concentrations of guanosine and g uanine that elicited xanthine oxidase-dependent trypanocidal activity were 30-270-fold lower than those of other purines requiring trypanosome-process ing which suggests differential processing by the parasites. (C) 2000 Elsev ier Science Inc. All rights reserved.