Soluble methane monooxygenase (MMO) isolated from Methylosinus trichosporium OB3b consists of three components: hydroxylase, reductase, and component B. The active-site diiron cluster of the hydroxylase has been studied with Mossbauer, ENDOR, and EPR spectroscopies. Móssbauer spectra of the oxidized cluster show that the two high-spin irons are antiferromagnetically coupled in accord with our preliminary study (Fox et al. J. Biol. Chem. 1988, 263, 10553-10556). Mossbauer studies also reveal the presence of two cluster conformations at pH 9. The excited-state S = 2 multiple! of the exchange-coupled cluster (Fe3+-Fe3+) gives rise to an integer-spin EPR signal near g = 8; this is the first quantitative study of such a signal from any system. Analysis of the temperature dependence of the g = 8 signal yields J -15 ± 5 cm™1 for the exchange-coupling constant (Htx = /Si-S2). This value is more than 1 order of magnitude smaller than those reported for the oxo-bridged clusters of hemerythrin and Escherichia coli ribonucleotide reductase (Hex = /Si-S2, J = 270 and 220 cm™1, respectively), suggesting that the bridging ligand of the hydroxylase cluster is not an unsubstituted oxygen atom. Móssbauer spectra of the hydroxylase in applied fields of up to 8 T reveal a paramagnetic admixture of a low-lying excited state into the ground singlet. Both the spectral shape and intensity are well represented by assuming that the spin expectation values for the cluster sites increase

The exchange of "0 between Hz*'0 and exogenously added '5N'602 which occurs during oxidation of ammonia by Nitrosomonas is shown to occur one oxygen at a time. Conditions in which the exchange is diminished (notably the presence of 14N02 and CCCP) allowed demonstration that water and dioxygen are each the source of one oxygen in nitrite produced from "NH3. The nitrite produced in the presence of "02 consisted of 67 and 0% 15N180160-and 1sN180180-, respectively. Analysis was made using the '80-isotope shift in "N-NMR.Nitrosomonas

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In huns, the left hemisphere of the brain is dominant for processing language. To assess the evolutionary origins of this neuropsychological mechanism, playback experiments were conducted on a large population of freeanging rhesus monkeys (Macaca mulad ). Playbacks provided an equal opportunity to orient the right or left ear toward the speaker. Results revealed that 61 of 80 adult rhesus favored the right ear (left hemisphere) when vocalizations from their own repertoire were heard but favored the left ear when listening to heterospecific vocalizations. In contrast, infants less than a year old showed no perceptual asymmetry for conspecific or heterospecific calls. Thus, like humans, adult rhesus monkeys also evidence left hemisphere dominance for processing speciesspecdfic vocalizations. The emergence of such asymmetry, however, may depend on both differential maturation of the two hemispheres and experience with the species-typical vocal repertoire.Humans show significant hemispheric asymmetries for communicative expression and perception, including left hemisphere dominance for spoken and signed language and right hemisphere dominance for face perception and expression (e.g., refs. 1-5). These hemispheric biases, however, must not be interpreted to mean that the less dominant hemisphere is quiet during a particular cognitive task. Thus, for example, the right hemisphere appears dominant with regard to processing the prosodic features of language (5). To understand the evolutionary origins of hemispheric asymmetries for communication in humans, it is necessary to determine whether phylogenetically proximal species, such as the monkeys and apes, process vocal and facial expressions from their own repertoire in similar ways. Present understanding of this problem is limited to two sets of studies. First, based on field studies of acoustic communication in Japanese macaques (6), psychophysical (7) and neurobiological (8) experiments have demonstrated that this species, but not closely related species, shows a left hemisphere bias for processing a single call type from the repertoire; these experiments mirrored those used on humans and involved playbacks of calls through headphones, measuring reaction time differences during a call discrimination task. Second, free-ranging rhesus macaques show a right hemisphere bias for the production of facial expressions, in terms of both timing and expressiveness (9).The present project sought to build on previous research by (i) testing individuals under natural conditions, (ii) using a large sample of individuals so that population-level asymmetries could be detected, (iii) recording subjects' responses to multiple call types within the repertoire so that the effects of variation in call meaning and affect (10-13) could be discerned, and (iv) testing young infants to determine the extent of developmental change in hemispheric function. Rhesus monkeys were selected as test subjects because of previous research on their communicative repertoire (9-13) and because of da...

Human tyrosine hydroxylase isoform 1 (hTH1) was expressed in Escherichia coli, purified as the apoenzyme, and reconstituted with iron. The resonance Raman spectra of hTHl complexed with dopamine, noradrenaline, tyramine, and catechol have been studied and compared to those obtained for TH isolated from bovine adrenal glands or rat phaeochromocytoma tissue. A TH-phenolate complex is reported for the first time. Using dopamine selectively '*O-labeled in the 3-position or both 3-and 4-hydroxy positions, we have been able to assign unambiguously the origin of the low-frequency vibration bands: the band at 631 cm-' involves the oxygen in the 4-position; the band at 592 cm-' involves the oxygen in the 3-position, and the band around 528 cm-' is shifted by both, suggesting a chelated mode vibration. A small shift of the 1275 cm-* band and no shift of the 1320 cm-' band were observed, showing that those two bands involve essentially ring vibrations of the catecholate moiety, rather than the C-0 stretching vibration as previously suggested. The spectrum of the catechol-&,-hTHl complex confirms this assignment. The resonance Raman spectra of the 54Fe, 56Fe, or 57Fe isotope-containing enzymes complexed with dopamine are virtually identical, showing that the component of the iron in the ~6 0 0 cm-' vibrations is too small to be observed. These results provide a better understanding of the Raman properties of iron-catecholate complexes in this enzyme, as well as in other metalloproteins and model compounds.

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Six-coordinated heme groups are involved in a large variety of electron transfer reactions because of their ability to exist in both the ferrous (Fe 2+ ) and ferric (Fe 3+ ) state without any large differences in structure. Our studies on hemes coordinated by two histidines (bis-His) and hemes coordinated by histidine and methionine (His-Met) will be reviewed. In both of these coordination environments, the heme core can exhibit ferric low spin EPR signals with large g max values (also called type I, highly anisotropic low spin, or highly axial low spin, HALS species) as well as rhombic EPR (type II) signals. In bis-His coordinated hemes rhombic and HALS envelopes are related to the orientation of the His groups with respect to each other such that (i) parallel His planes results in a rhombic signal and (ii) perpendicular His planes results in a HALS signal. Correlation between the structure of the heme and its ligands for heme with His-Met axial ligation and ligand-field parameters, as derived from a large series of cytochrome c variants, show, however, that for such a combination of axial ligandsthere is no clear-cut difference between the large g max and the "small g-anisotropy" cases as a result of the relative Met-His arrangements. Nonetheless, a new linear correlation links the average shift <δ> of the heme methyl groups with the g max values.

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