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Bacterial diheme peroxidases represent a diverse enzyme family with functions that range from hydrogen peroxide (H2O2) reduction to post-translational modifications. By implementing a sequence similarity network (SSN) of the bCCP_MauG superfamily, we present the discovery of a unique diheme peroxidase BthA conserved in all Burkholderia. Using a combination of magnetic resonance, near-IR and Mössbauer spectroscopies and electrochemical methods, we report that BthA is capable of generating a bis-Fe(IV) species previously thought to be a unique feature of the diheme enzyme MauG. However, BthA is not MauG-like in that it catalytically converts H2O2 to water, and a 1.54-Å resolution crystal structure reveals striking differences between BthA and other superfamily members, including the essential residues for both bis-Fe(IV) formation and H2O2 turnover. Taken together, we find that BthA represents a previously undiscovered class of diheme enzymes, one that stabilizes a bis-Fe(IV) state and catalyzes H2O2 turnover in a mechanistically distinct manner.

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UNLABELLED: Pyruvate, a central intermediate in the carbon fixation pathway of methanogenic archaea, is rarely used as an energy source by these organisms. The sole exception to this rule is a genetically uncharacterized Methanosarcina barkeri mutant capable of using pyruvate as a sole energy and carbon source (the Pyr(+) phenotype). Here, we provide evidence that suggests that the Pyr(+) mutant is able to metabolize pyruvate by overexpressing pyruvate ferredoxin oxidoreductase (por) and mutating genes involved in central carbon metabolism. Genomic analysis showed that the Pyr(+) strain has two mutations localized to Mbar_A1588, the biotin protein ligase subunit of the pyruvate carboxylase (pyc) operon, and Mbar_A2165, a putative transcriptional regulator. Mutants expressing the Mbar_A1588 mutation showed no growth defect compared to the wild type (WT), yet the strains lacked pyc activity. Recreation of the Mbar_A2165 mutation resulted in a 2-fold increase of Por activity and gene expression, suggesting a role in por transcriptional regulation. Further transcriptomic analysis revealed that Pyr(+) strains also overexpress the gene encoding phosphoenolpyruvate carboxylase, indicating the presence of a previously uncharacterized route for synthesizing oxaloacetate in M. barkeri and explaining the unimpaired growth in the absence of Pyc. Surprisingly, stringent repression of the por operon was lethal, even when the media were supplemented with pyruvate and/or Casamino Acids, suggesting that por plays an unidentified essential function in M. barkeri. IMPORTANCE: The work presented here reveals a complex interaction between anabolic and catabolic pathways involving pyruvate metabolism in Methanosarcina barkeri Fusaro. Among the unexpected findings were an essential role for the enzyme pyruvate-ferredoxin oxidoreductase and an alternate pathway for synthesis of oxaloacetate. These results clarify the mechanism of methanogenic catabolism of pyruvate and expand our understanding of carbon assimilation in methanogens.

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OBJECTIVE: Compare the influence of ethnicity in the prevalence of osteopenia and osteoporosis in various Mexican populations using two normal dual X-ray absorptiometry (DXA) reference databases: manufacturer's incorporating US Hispanic population and a normal mestizo Mexican population. MATERIAL AND METHODS: MMP included 9 946 subjects participating in an ongoing long-term cohort study focusing on lifestyle and chronic diseases, of which 6 487 MMP males and females aged 7 to 80 years were the normal subjects used to determine bone density T- and Z-scores, following WHO criteria, and peak bone mass values. Abnormal bone mass density values estimated by the manufacturer's and peak bone mass reference values were compared. RESULTS AND CONCLUSIONS: Our results show that by using the manufacturer's T-score values in the mestizo Mexican population we are underestimating the number of abnormal bone mass BMD populations.

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OBJECTIVE: Compare the influence of ethnicity in the prevalence of osteopenia and osteoporosis in various Mexican populations using two normal dual X-ray absorptiometry (DXA) reference databases: manufacturer's incorporating US Hispanic population and a normal mestizo Mexican population. MATERIAL AND METHODS: MMP included 9 946 subjects participating in an ongoing long-term cohort study focusing on lifestyle and chronic diseases, of which 6 487 MMP males and females aged 7 to 80 years were the normal subjects used to determine bone density T- and Z-scores, following WHO criteria, and peak bone mass values. Abnormal bone mass density values estimated by the manufacturer's and peak bone mass reference values were compared. RESULTS AND CONCLUSIONS: Our results show that by using the manufacturer's T-score values in the mestizo Mexican population we are underestimating the number of abnormal bone mass BMD populations.

OBJETIVO: Comparar la influencia de la etnicidad en la prevalencia de osteopenia y osteoporosis en varias poblaciones mexicanas utilizando dos bases de referencia normal de densitometría de rayos X (DXA): referencia del fabricante que incorpora hispanos en Estados Unidos y datos de una población mestiza mexicana. MATERIAL Y MÉTODOS: Un total de 9 946 sujetos de población mestiza mexicana participantes en una cohorte de largo plazo dirigida al estudio de estilos de vida y ocurrencia de enfermedades crónicas; de los cuales 6 487 sujetos sanos de ambos sexos, con edad entre los 7 y los 80 años, fueron utilizados para determinar los valores T, Z, de acuerdo a los criterios de la OMS, así como a los valores de masa ósea pico. Se compararon los casos de densidad mineral ósea anormal de acuerdo a los valores de referencia del fabricante y los valores de masa ósea pico de la población mestiza. RESULTADOS Y CONCLUSIÓN: Las bases de referencia del fabricante subestima significativamente el número de casos con densidad mineral ósea anormal en la población mestiza mexicana.

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