Topography of the C terminus of cytochrome b5 tightly bound to dimyristoylphosphatidylcholine vesicles.
Cytochrome b5 holoenzyme was bound asymmetrically in the tightly bound form to small unilamellar dimyristoylphosphatidylcholine vesicles. [3H]Taurine, a membrane-impermeant nucleophile, was added to the external medium and was then cross-linked to cytochrome carboxyl residues by the addition of a water-soluble carbodiimide. Nonpolar peptide was isolated after trypsin digestion of taurine-labeled apocytochrome b5 and contained 1.7-1.9 residues of taurine. The C-terminal tetrapeptide containing residues Thr130-Asn133 was generated by chymotryptic hydrolysis of radiolabeled nonpolar peptide and was purified by gel filtration and ion exchange chromatography. Amino acid analysis of the C-terminal tetrapeptide showed that about 1.6 mol of taurine was cross-linked per mol of peptide. When the experiment was performed with taurine trapped inside the vesicles, no cross-linking was observed. The results suggest that when cytochrome b5 holoenzyme is bound to vesicles in the tight binding form, the C terminus is located on the external surface of the vesicles.
Arinç
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E
Department of Biochemistry, University of Connecticut Health Center, Farmington 06032.
Rzepecki
L M
LM
Strittmatter
P
P
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism; D003573:Cytochrome b Group / Q000032:analysis*; D015786:Cytochromes b5; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010446:Peptide Fragments / Q000032:analysis; D013654:Taurine / Q000378:metabolism
D000596:Amino Acids; D003573:Cytochrome b Group; D010446:Peptide Fragments; D013654:Taurine; D015786:Cytochromes b5; D002918:Chymotrypsin; D004134:Dimyristoylphosphatidylcholine