Cell Language Theory, The: Connecting Mind And Matter

The Bhopalator 147

“6x9” b2861 The Cell Language Theory: Connecting Mind and Matter

Fig

ure 3.40

The

Helsinki mechanism

of cytochrome oxidase proton pump. The kinetic mechanism of the proton pumping driven by oxygen

reduction in cytochrome c oxidase. The neologism is adopted here first for the convenience of future reference and second to recognize the many important contributions made by the research group in Helsinki headed by Professor Marten Wikstr

őm toward our understanding of

the phenomenon of

electron-coupled proton transport

(ECPT) in membrane enzyme systems. (a) Cytochrome c oxidase consisting of three

subunits (SU) represented as colored transparent ribbons — SU I in blue, SU II in red, and SU III in orange. There are two proton channels colored represented as blue arrows — the D channel involving aspartic acid residue D91 to glutamic acid residue E242 leading to either Proton Loading Site (PLS) or BNC (binuclear center) depending on whether or not electron is transferred from cytochrome c to BNC via heme a (see orange arrow), and the K channel involving lysine residue K319 and ending up at BNC [118]. (b) The mechanism (or kinemat

ics) of the coupling between the water reduction chemistry and the trans-membrane proton pumping in cytochrome c oxidase. Four electrons are transferred one by one from cytochrome c on the intermembrane (or positive) side of the inner membrane to the binuclear center (BNC) via a series of electron carriers, Cu

, heme a, heme aA

, and Cu 3

. These electrons combine with four protons transferred from the matrix (or B

negative) side of the membrane via the so-called K-channel to form two molecules of water. The free energy released from this reaction drives the trans-membrane movement (i.e., proton pumping) from the matrix to the inter-membrane space, which later drive the synthesis of one molecule of ATP catalyzed by the F

F 1

–ATP synthase (see 0

Fig

ure 3.35). Retrieved from http://www.helsinki.fi/lehdet/uh/liite01n.htm.

(c) The kinetic mechanism of the trans-membrane proton movement through cytochrome c oxidase driven by the free energy released from the reduction of oxygen to water. The key steps are (i) the binding of oxygen to heme a

to produce BNC state A, (ii) the splitting of dioxygen 3

to two oxygen atoms to form state P

, (iii) the first electron transfer from cytochrome c to the tyrosyl radical in BNC to produce tyrosyl M

anion in state P

resulting in one proton (black) consumption by the oxygen reduction chemistry and one proton (blue) pumped across R

through the enzyme, (iv) the second electron transfer from cytochrome c to heme a

to produce state O 3

, (v) the third electron transfer from H

cytochrome c to Cu

to produce state EB

, and finally (vi) the fourth electron transfer from cytochrome c to heme aH

to produce state R ready 3

to initiate the next cycle of the oxygen reduction-driven proton pumping. Reproduced from [118, 119].

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