A Kinetic Study of the pH‐Dependent Properties of the Ferric Undecapeptide of Cytochrome c (Microperoxidase)

Abstract

The ferric form of the haem undecapeptide, derived from horse cytochrome c by peptic digestion, undergoes at least three pH-induced transitions with pK values of 3.4, 5.8 and 7.6. Temperaturejump experiments suggest that the first of these is due to the binding of a deprotonated imidazole group to the ferric iron while the second and third arise from the binding of the two available amino groups present (the a-NH2 of valine and the E -N H~ of lysine).Molecular models indicate that steric restraints on the peptide dictate that these amino groups may only coordinate to iron atoms via intermolecular bonds, thus leading to the polymerization of the peptide.Cyanide binding studies are in agreement with these conclusions and also yield a value of 3.6 x lo6 M-' s-' for the intrinsic combination constant of CN-anion with the haem.A model is proposed which describes the pH-dependent properties of the ferric undecapeptide.

Peroxidase model electrodes: Self-mediation of heme peptide multilayer-modified electrodes and its application to biosensing with adjustable dynamic range

“…It is known that dimerization and oligomerization of HP give rise to such a red-shift. HP was reported to form a dimer and oligomers by coordination of the amino group of the lysine or the terminal valine residue to the heme in higher pH solutions [32]. At higher HP concentrations, it was reported to form a l-oxo dimer by coordination of the sixth coordination sites of the hemes through oxygen [33].…”

“…Afterward, the electrode was stored at 4°C for 2 days and thoroughly rinsed with distilled water for removal of the solution and excess HP molecules. Surface coverage of HP was determined by spectrophotometric measurements (MCPD-3000 and MC2530, Otsuka Electronics Co. Ltd.) with the maximum mole extinction coefficient of e = 176 mM À1 cm À1 [8,32]. All other reagents were of at least analytical grade and used without further purification.…”

Effect of Tris on catalytic activity of MP-11

“…The concentrations of MP-11 were estimated according to [19] and purified samples were stored at 4 -C. All physiological solutions [20] in our experiments in vitro were maintained at pH 7.4 and ionic strength 0.1 M by adding HCl (or NaOH) and NaCl into Tris (or MP-11) aqueous solution. Triple distilled water was used throughout this work.…”

Study on mechanism of interaction between Eu3+ and microperoxidase-11

“…The concentration of the MP-11 solutions was measured using the UV-vis absorption spectroscopic technique with ε MP-11 395 = 176 mM −1 cm −1 [25]. According to Taylor's method [26], EuCl 3 was obtained from Eu 2 O 3 (>99.9%).…”