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Pulse radiolysis studies on galactose oxidase

Lookup NU author(s): Craig Wright, Mark Twitchett, Emeritus Prof Alfred Sykes

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Abstract

Single-Cu-containing galactose oxidase in the GOasesemi state (CuII, no Tyr radical) reacts with pulse radiolysis generated formate radicals CO2.- to give an intermediate UV-vis spectrum assigned as RSSR.-, peak at 450 nm (ε = 8100 M-1 cm-1). From a detailed kinetic analysis at 450 nm, pH 7.0, the following steps have been identified. First the strongly reducing CO2.- (-1.9V) reduces GOasesemi (k0 ≥ 6.5 × 108 M-1 s-1) to a species GOasesemi.- This is followed by biphasic reactions (i) GOasesemi.- + GOasesemi (k1 = 1.6 × 107 M-1 s-1) to give GOasesemi + P.- and (ii) P.- + GOasesemi (k2 = 6.7 × 106 M-1 s-1) to give GOasesemiRSSR.-. There are no significant absorbance changes for the formation of GOasesemi.- and P.-, which are CuI (or related) species. However, GOasesemiRSSR.- has an absorption spectrum which differs significantly from that of GOasesemi. The 450 nm peak is characteristic of an RSSR.- radical with two cysteines in close sequence proximity and is here assigned to Cys515-Cys518, which is at the GOase surface and 10.2 Å from the Cu. On chemical modification of the RSSR group with HSPO32- to give RSSPO3H- and RS-, absorbance changes are ∼50% of those previously observed. The decay of RSSR.- (0.17 s-1) results in the formation of GOasered. No RSSR.- formation is observed in the reaction of GOasesemi Tyr495Phe with CO2.-, and a single process giving GOaseredTyr495Phe occurs. Similarly in the reaction of GOaseox with CO2.-, a single-stage reaction gives GOasesemi.

Publication metadata

Author(s): Borman CD, Wright C, Twitchett MB, Salmon GA, Sykes AG

Publication type: Article

Publication status: Published

Journal: Inorganic Chemistry

Year: 2002

Volume: 41

Issue: 8

Pages: 2158-2163

ISSN (print): 0020-1669

ISSN (electronic): 1520-510X

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/ic0109344

DOI: 10.1021/ic0109344

PubMed id: 11952369

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