The Alkaline Transition of Bis(N-acetylated) Heme Undecapeptide

Abstract

Alkaline forms of the ferric bis(N-acetylated) heme undecapeptide of cytochrome c (N-ac-HUP) and some of its derivatives have been studied by electronic absorption and electron paramagnetic resonance spectroscopies. Surprisingly, even at pH >12, no evidence could be found for the formation of a hydroxyl ion adduct, in direct contrast to a previous report concerning ferric heme peptides encapsulated in detergent micelles (Mazumdar et al. Inorg. Chem. 1991, 30, 700-705). A spectroscopically determined pK(a) of approximately 9 is assigned to the deprotonation of the constituent histidine ligand of heme iron in N-ac-HUP. The present findings are not entirely in keeping with those of an earlier study concerning the properties of N-acetylated heme octapeptide (Wang et al. J. Biol. Chem. 1992, 35, 15310-15318), the differences observed being attributed to the buffering media employed in the two investigations. The implications of the current results in relation to a better understanding of the alkaline transitions observed in hemoglobins and myoglobins is considered.

Modified Microperoxidases Exhibit Different Reactivity Towards Phenolic Substrates

“…Similar behavior was reported for MP11 which, for the intermolecular coordination to iron( III ), uses the α‐NH 2 of the Val residue or the ε ‐NH 2 of the Lys residue 26. 28 Meanwhile, for the other MP catalysts, the spin properties do not depend on the complex concentration. Moreover, up to 10 μ M , the systems show good adherence to the Lambert–Beer law; this indicates a prevalent monomeric form within this concentration range (data not shown).…”

A mitochondria-targeted inhibitor of cytochrome c peroxidase mitigates radiation-induced death

“…However, when IOA was added to the cyt c /TOCL complex, the EPR spectrum revealed the presence of another low-spin species (g z =2.97, g y =2.27, g x ~1.5, Fig. 3f) with g-values entirely consistent with His/imidazole coordination 20,21 . This signal was broadened on the low-field side, suggesting a combination of the native ferri-cyt c and a His/imidazole form.…”

Covalent Modifications of Hemoglobin by Nitrite Anion: Formation Kinetics and Properties of Nitrihemoglobin

“…It is clear by inspection of Figure 6 that any differences between the alkaline transitions of metNHb and metHb, or the EPR and absorption-derived estimates of the associated p K a , are within the experimental uncertainty. Variations in the alkaline transitions of heme proteins are undoubtedly more a consequence of heme-pocket properties than the heme group per se (17). It follows that, at least in terms of this particular functional characteristic, the metNHb heme pocket seems unperturbed compared to that of metHb.…”

“…Alkaline Transition Measurements. The alkaline transition of metNHb was determined using a minor variation of a procedure described previously (17). MetNHb was prepared by adding a slight excess of potassium ferricyanide to ∼0.03 µM solutions of oxyNHb, and the resulting solution was then dialyzed against 0.3 M NaCl (2 days, 4 °C, 3 × 2.0 L buffer changes).…”