Rate constants proton transfer from cytochrome

Table 18 Rate constants for the proton transfer from [cytochrome c] (n = 7-9) to alkylamines"...

The proton transfer from multiply charged [cytochrome c] " (n = 7-9) to (/ )- and (5)-2-butylamine show a significant enantioselectivity." " Ions [cytochrome n = l-9) were produced by ESI and introduced into the analyzer cell of a FT-ICR containing an alkylamine, i.e., (/ )- and (5)-2-butyIamine, 1-propylamine, or tert-butylamine. Rate constants for the proton transfer are listed in Table 18. 

In native reaction centers, as shown in Fig. 6 (A), the first photon causes the transfer of one electron from P to Qa and then to Qq [with rate constant itAB(i)]while is reduced hy a cytochrome in 1 ps. The end product of the first photoact is P-Qa Qb The absorption of a second photon causes this process to be repeated, and the resulting P Qa Qb picks up a proton, (1), to form P-Q (QbH). 

M. The data do not, however, allow a distinction to be drawn between electron transfer at the bridging oxygen, terminal water, or porphyrin periphery. In the presence of histidine, the major species is [Fe (TMpyP)(his)a], which is reduced by ascorbate in an inner-sphere pathway involving protonation and dissociation of one of the axial histidine ligands. The rate constant for histidine dissociation, 25.2 s, is remarkably similar to the rate of dissociation of methionine-80, 60 s, in the ascorbate reduction of cytochrome c. Autoreduction of [Fe TPP] in the presence of piperidine proceeds by proton abstraction from co-ordinated piperidine as shown by a large isotope effect in the reaction. Electron transfer produces iron(ii) and a nitrogen radical. 

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