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Spemannstrasse 34, D7400 Tubingen and 'Max-Planck-Institut fiir Biochemie, D8033 Martinsried, FRG Communicated by P.Overath A transferrin-binding protein (TFBP) with an apparent molecular weight of 42 kd was purified from detergentsoluble membrane proteins of bloodstream forms of Trypanosoma brucei. The protein is not expressed in the insect-borne stage of the parasite's life-cycle. Purified TFBP can be converted from an amphiphilic to a hydrophilic form by cleavage with T.brucei glycosylphosphatidylinositol (GPI)-specific phospholipase C, demonstrating that the C-terminus is modified by a GPImembrane anchor. The TFBP is encoded by an expression-site-associated gene [ESAG 6 in the nomenclature of Pays et al. (1989) Cell, 57,[835][836][837][838][839][840][841][842][843][844][845] which is under the control of the promoter transcribing the expressed variant surface glycoprotein gene. The possible function of TFBP as a receptor for the uptake of transferrin in bloodstream forms is discussed.

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The respiratory chain NADH:ubiquinone oxidoreductase (NADH dehydrogenase or Complex I) of mitochondria comprises some 30 different subunits, and one FMN and 4 or 5 iron-sulfur clusters as internal redox groups. The bacterial glucose dehydrogenase, which oxidizes glucose to gluconolactone in the periplasmatic space and transfers the electrons to ubiquinone, is a single polypeptide chain with pyrolloquinoline quinone as the only redox group. We report here that the two different enzymes have the same ubiquinone binding domain motif and we discuss the predicted membrane folding of this domain with regard to its role in the proton translocating function of the two enzymes.