Influence of the heme distal pocket on nitrite binding orientation and reactivity in Sperm Whale myoglobin

Tse, Wilford, Whitmore, Nathan, Cheesman, Myles R. and Watmough, Nicholas J. (2021) Influence of the heme distal pocket on nitrite binding orientation and reactivity in Sperm Whale myoglobin. Biochemical Journal, 478 (4). pp. 927-942. ISSN 0264-6021

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Nitrite binding to recombinant wild-type Sperm Whale myoglobin (SWMb) was studied using a combination of spectroscopic methods including room-temperature magnetic circular dichroism. These revealed that the reactive species is free nitrous acid and the product of the reaction contains a nitrite ion bound to the ferric heme iron in the nitrito- (O-bound) orientation. This exists in a thermal equilibrium with a low-spin ground state and a high-spin excited state and is spectroscopically distinct from the purely low-spin nitro- (N-bound) species observed in the H64V SWMb variant. Substitution of the proximal heme ligand, histidine-93, with lysine yields a novel form of myoglobin (H93K) with enhanced reactivity towards nitrite. The nitrito-mode of binding to the ferric heme iron is retained in the H93K variant again as a thermal equilibrium of spin-states. This proximal substitution influences the heme distal pocket causing the pKa of the alkaline transition to be lowered relative to wild-type SWMb. This change in the environment of the distal pocket coupled with nitrito-binding is the most likely explanation for the 8-fold increase in the rate of nitrite reduction by H93K relative to WT SWMb.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Faculty of Science > School of Biological Sciences
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Depositing User: LivePure Connector
Date Deposited: 05 Mar 2021 00:44
Last Modified: 20 Apr 2023 20:32
DOI: 10.1042/BCJ20200596


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