ISSN:
1574-6968
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Biologie
Notizen:
Procyclic forms of Trypanosoma brucei possess a phosphatase activity on their external cell surface. This activity, while it dephosphorylates [32P]phosphocasein, is inhibited weakly by NaF and tartrate but strongly by vanadate. In this work, we describe the presence of an external phosphatase activity in intact bloodstream forms of T. brucei. With p-nitrophenyl phosphate (pNPP) as substrate, these intact cells produced 3–5 nmol pNP min−1 mg−1, linearly for up to at least 30 min. The activity was not significantly increased by Mg2+, Mn2+, Ca2+ and Co2+, but was inhibited by vanadate, NaF, p-chloromercuribenzoate and Zn2+ and was insensitive to okadaic acid. Membrane-enriched fractions of parasites contained an acid phosphatase activity, with a pH optimum in the range of 4.5–5.5. This activity hydrolyzed phosphotyrosine (40 nmol phosphate min−1 mg−1) better than phosphothreonine or phosphoserine. Partial purification of this phosphatase yielded a single activity band following gel electrophoresis, a Km value of 0.29 mM with pNPP and was insensitive to the Fe2+/H2O2/ascorbate system.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1016/S0378-1097(03)00091-0
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