The Alkaline Transition of Bis(N-acetylated) Heme Undecapeptide.
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.
Carraway
Angela D.
AD
Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487-0336, Department of Mathematical and Physical Sciences, Northwestern State University of Louisiana, Natchitoches, Louisiana 71497, Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, and Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213.
Miller
Gregory T.
GT
Pearce
Linda L.
LL
Peterson
Jim
J