Discussion Paper

Specific cation binding site in mammalian cytochrome oxidase

“…The situation is complicated by a possibility of energy-linked increase in a¤nity of the site for cations. There is some evidence for energy-linked protonation of the site [5,6], but energy-dependence of Ca P or Na binding with COX remain to be studied.…”

“…More than 20 years ago Wikstrom and collaborates discovered that Ca P shifts absorption spectrum of reduced heme a to the red in rat liver and bovine heart COX [5,6]. The ¢nding was con¢rmed by P. Nicholls [7] and, later on, in this group [8].…”

“…Ionic speci¢city of the calcium e¡ect is peculiar. It was reported initially that none of other metal cations including Eu Q , La Q , Mg P , Sr P , Zn P , Ba P , Na , K or Li could mimick or in£uence the Ca P -induced shift [10], but a very similar shift, mutually exclusive with the calcium-dependent one, was induced by protons [5,6,10,11]. It was proposed that Ca P and H compete for binding with the carboxylic group of propionate substituent in heme a [10].…”