{"doi":"10.1007/s00775-022-01953-4","title":"Determination of the iron(IV) local spin states of the Q intermediate of soluble methane monooxygenase by Kβ X-ray emission spectroscopy","abstract":"Abstract Soluble methane monooxygenase (sMMO) facilitates the conversion of methane to methanol at a non-heme Fe IV 2 intermediate MMOH Q , which is formed in the active site of the sMMO hydroxylase component (MMOH) during the catalytic cycle. Other biological systems also employ high-valent Fe IV sites in catalysis; however, MMOH Q is unique as Nature’s only identified Fe IV 2 intermediate. Previous 57 Fe Mössbauer spectroscopic studies have shown that MMOH Q employs antiferromagnetic coupling of the two Fe IV sites to yield a diamagnetic cluster. Unfortunately, this lack of net spin prevents the determination of the local spin state ( S loc ) of each of the irons by most spectroscopic techniques. Here, we use Fe Kβ X-ray emission spectroscopy (XES) to characterize the local spin states of the key intermediates of the sMMO catalytic cycle, including MMOH Q trapped by rapid-freeze-quench techniques. A pure XES spectrum of MMOH Q is obtained by subtraction of the contributions from other reaction cycle intermediates with the aid of Mössbauer quantification. Comparisons of the MMOH Q spectrum with those of known S loc = 1 and S loc = 2 Fe IV sites in chemical and biological models reveal that MMOH Q possesses S loc = 2 iron sites. This experimental determination of the local spin state will help guide future computational and mechanistic studies of sMMO catalysis. Graphical abstract","journal":"JBIC Journal of Biological Inorganic Chemistry","year":2022,"id":262304,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":14,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9571,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2022-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":307006,"name":"R. Banerjee","orcid":"0000-0002-8193-7369","position":1,"is_corresponding":false},{"id":917659,"name":"Derek B. Rice","orcid":"0000-0002-4881-421X","position":2,"is_corresponding":false},{"id":918076,"name":"Olivia McCubbin Stepanic","orcid":null,"position":3,"is_corresponding":false},{"id":307018,"name":"John D. Lipscomb","orcid":"0000-0002-8158-5594","position":4,"is_corresponding":false},{"id":310519,"name":"Serena DeBeer","orcid":"0000-0002-5196-3400","position":5,"is_corresponding":false},{"id":397229,"name":"George E. Cutsail","orcid":"0000-0002-7378-9474","position":0,"is_corresponding":true}],"reference_count":82,"raw_metadata":null,"created_at":"2026-07-19T00:26:20.717229Z","pmid":"35988092","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}