Localization of 3'-nucleotidase and calcium-dependent endoribonuclease in the plasma-membrane of Trypanosoma brucei.

We have characterized a 3'-nucleotidase activity of T. brucei. The enzyme has a pH optimum of 8.7, is inactivated by chelating agents and stimulated by divalent cations. It is inhibited by Zn2+, Mn2+, pyrophosphate and the trypanocidal drug suramin for which it has a Ki of 3 microM. From cell fractionation experiments it is concluded that the enzyme is located in the plasma membrane. Alkaline 3'-endoribonuclease is also located in the plasma membrane of T. brucei and this activity shares a great number of properties with the 3'-nucleotidase activity, including its sensitivity to suramin. The possibility that both 3'-nucleotidase and endonuclease activities are catalyzed by the same enzyme cannot be excluded.