Ion binding to lysine-modified derivatives of cytochrome c.
The effect of Cl- and K+ ions on the apparent equilibrium constant of the reaction between horse ferricytochrome c and potassium ferrocyanide was studied. Unmodified cytochrome was compared with two lysine-modified derivatives. One, guanidinated, had all lysyl groups converted to homoarginine (but retained the same positive charge); the other was trinitrophenylated at one lysine (measured spectrophotometrically). Both modified derivatives had a somewhat larger equilibrium constant in the reaction of the reduced protein with ferricyanide, but, unlike trifluoroacetylated cytochrome c (which has a negative charge), the redox properties were not dramatically different. The native protein and the lysine-modified cytochromes showed differential K+ binding in Tris-cacodylate buffer at constant ionic strength (0.003-0.005 M). More K+ was bound to ferrocytochrome c. This redox-linked binding, however, was unaffected by modification of lysine. All three derivatives also showed redox-linked differential Cl- ion binding (more Cl- ion was bount to ferricytochrome); however, in this case, the binding was reduced in the lysine-modified molecules. This was interpreted as loss of a single anion site. This anion site critically depends on one or a few lysines which are more reactive with trinitrobenzene sulfonate.
D001665:Binding Sites; D002712:Chlorides; D003574:Cytochrome c Group; D005295:Ferrocyanides; D006146:Guanidines; D008239:Lysine; D009994:Osmolar Concentration; D011188:Potassium; D011485:Protein Binding; D014301:Trinitrobenzenes
D002712:Chlorides; D003574:Cytochrome c Group; D005295:Ferrocyanides; D006146:Guanidines; D014301:Trinitrobenzenes; D008239:Lysine; D011188:Potassium