Transcriptional programming of social hierarchy

In this issue of Neuron, Choi and colleagues1 uncover the direct role of the transcription factor Pou3f1 in regulating dominance hierarchy in mice. Pou3f1 accomplishes this role via its action in specific prefrontal projection neurons that regulate behaviors associated with low social status.

A transcriptomic axis predicts state modulation of cortical interneurons

Transcriptomics has revealed that cortical inhibitory neurons exhibit a great diversity of fine molecular subtypes^1-6, but it is not known whether these subtypes have correspondingly diverse patterns of activity in the living brain. Here we show that inhibitory subtypes in primary visual cortex (V1) have diverse correlates with brain state, which are organized by a single factor: position along the main axis of transcriptomic variation. We combined in vivo two-photon calcium imaging of mouse V1 with a transcriptomic method to identify mRNA for 72 selected genes in ex vivo slices. We classified inhibitory neurons imaged in layers 1-3 into a three-level hierarchy of 5 subclasses, 11 types and 35 subtypes using previously defined transcriptomic clusters³. Responses to visual stimuli differed significantly only between subclasses, with cells in the Sncg subclass uniformly suppressed, and cells in the other subclasses predominantly excited. Modulation by brain state differed at all hierarchical levels but could be largely predicted from the first transcriptomic principal component, which also predicted correlations with simultaneously recorded cells. Inhibitory subtypes that fired more in resting, oscillatory brain states had a smaller fraction of their axonal projections in layer 1, narrower spikes, lower input resistance and weaker adaptation as determined in vitro⁷, and expressed more inhibitory cholinergic receptors. Subtypes that fired more during arousal had the opposite properties. Thus, a simple principle may largely explain how diverse inhibitory V1 subtypes shape state-dependent cortical processing.

Parenting as a model for behavioural switches

Adaptability to ethologically relevant cues is fundamental for social interactions. As such, reproductive success relies on the ability of an animal to transition between parental and nonparental states. Though driven by genetically pre-programmed circuits, these instinctive repertoires are reshaped by internal state and experience, making parenting a robust model for the study of behavioural flexibility. As a functional wiring diagram for parenting emerges in mice, we are well placed to identify neural substrates and posit associated mechanisms underlying caregiving transitions. In this review, we discuss the importance of comprehensively characterising behaviour, highlight the role of shared circuit elements for behavioural malleability and explore plastic mechanisms that might guide switches between parental and nonparental repertoires.

Single-cell molecular and developmental perspectives of sexually dimorphic circuits underlying innate social behaviors

While single-cell transcriptomics in the brain has uncovered a vast diversity of neural cell types in unprecedented detail, it is becoming increasingly urgent to address what exactly their functional roles are in the context of circuits and behavior. In this review, we discuss the molecular profiling of cell types in circuits underlying social behaviors in mice as a prominent case study. We first highlight key roles of molecularly identified sensory and downstream neurons involved in sexually dimorphic behaviors. We then propose future opportunities to define cell types using multimodal criteria, especially gene expression, physiology, as well as the developmental origin, to advance our understanding of these circuits.

Record-high sensitivity compact multi-slot sub-wavelength Bragg grating refractive index sensor on SOI platform

In this paper, a high sensitivity compact multi-slot sub-wavelength Bragg grating refractive index (RI) sensor was investigated. The structural parameters were optimized for higher sensitivity to RI change of the surrounding medium from viewpoints of a wavelength shift, an extinction ratio and a transmission loss, and a record-high sensitivity was experimentally demonstrated with a compact size. In this sensor, the first side-lobe at the Bragg grating (BG) stop-band end was focused as a sensing peak wavelength for moderate transmission loss and efficient sensing. To realize the compactness, a period count of the BG was kept as small as 20. By increasing the RI of the surrounding medium, the sensing peak shifts toward a longer wavelength side; thus due to the high sharpness and easy tracing of the first side-lobe, the device worked as an efficient RI sensor. The structural optimization was carried out by using 3D finite-difference time-domain (FDTD) simulation approach, and also influences of the structural parameters to sensitivities were discussed. Based on these optimized parameters, the devices were fabricated using the lift-off technique. By exposing the sensor to various liquid samples with different RIs such as pure water, sugar-dissolved water with various concentrations, acetone and isopropyl alcohol (IPA), a record-high sensitivity of 730 nm/RIU was attained for a sensor fabricated on SOI platforms with a length of as small as 9.5 µm and a transmission loss of 3 dB.

Multisensory Logic of Infant-Directed Aggression by Males

Newborn mice emit signals that promote parenting from mothers and fathers but trigger aggressive responses from virgin males. Although pup-directed attacks by males require vomeronasal function, the specific infant cues that elicit this behavior are unknown. We developed a behavioral paradigm based on reconstituted pup cues and showed that discrete infant morphological features combined with salivary chemosignals elicit robust male aggression. Seven vomeronasal receptors were identified based on infant-mediated activity, and the involvement of two receptors, Vmn2r65 and Vmn2r88, in infant-directed aggression was demonstrated by genetic deletion. Using the activation of these receptors as readouts for biochemical fractionation, we isolated two pheromonal compounds, the submandibular gland protein C and hemoglobins. Unexpectedly, none of the identified vomeronasal receptors and associated cues were specific to pups. Thus, infant-mediated aggression by virgin males relies on the recognition of pup's physical traits in addition to parental and infant chemical cues.

Dopamine neurons projecting to the posterior striatum form an anatomically distinct subclass

Combining rabies-virus tracing, optical clearing (CLARITY), and whole-brain light-sheet imaging, we mapped the monosynaptic inputs to midbrain dopamine neurons projecting to different targets (different parts of the striatum, cortex, amygdala, etc) in mice. We found that most populations of dopamine neurons receive a similar set of inputs rather than forming strong reciprocal connections with their target areas. A common feature among most populations of dopamine neurons was the existence of dense ‘clusters’ of inputs within the ventral striatum. However, we found that dopamine neurons projecting to the posterior striatum were outliers, receiving relatively few inputs from the ventral striatum and instead receiving more inputs from the globus pallidus, subthalamic nucleus, and zona incerta. These results lay a foundation for understanding the input/output structure of the midbrain dopamine circuit and demonstrate that dopamine neurons projecting to the posterior striatum constitute a unique class of dopamine neurons regulated by different inputs.

DOI:http://dx.doi.org/10.7554/eLife.10032.001

Most neurons send their messages to recipient neurons by releasing a substance called a ‘neurotransmitter’ that binds to receptors on the target cell. The sites of this type of signal transmission are called synapses. Some small populations of neurons modulate the activity of hundreds or thousands of these synapses all across the brain by releasing ‘neuromodulators’ that affect how they work. These neuromodulators are essential because they broadcast information that is likely to be useful to many brain regions, like a ‘news channel’ for the brain.

One important neuromodulator in the mammalian brain is dopamine, which contributes to motivation, learning, and the control of movement. Clusters of cells deep in the brain release dopamine, and people with Parkinson's disease gradually lose these cells. This makes it increasingly difficult for their brains to produce the correct amount of dopamine, and results in symptoms such as tremors and stiff muscles.

Individual dopamine neurons typically send information to a single part of the brain. This suggests that dopamine neurons with different targets might have different roles. To explore this possibility, Menegas et al. classified dopamine neurons in the mouse brain into eight types based on the areas to which they project, and then mapped which neurons send input signals to each type. These inputs are likely to shape the activity of each type (that is, their ‘message’ to the rest of the brain). The mapping revealed that most dopamine neurons do not receive substantial input from the area to which they project (i.e., they do not form ‘closed loops’). Instead, most of their input comes from a common set of brain regions, including a particularly large number of inputs from the ventral striatum.

However, Menegas et al. found one exception. Dopamine neurons that target part of the brain called the posterior striatum receive relatively little input from the ventral striatum. Their input comes instead from a set of other brain structures, and in particular from a region called the subthalamic nucleus. Electrical stimulation of the subthalamic nucleus can help to relieve the symptoms of Parkinson's disease. Therefore, the results presented by Menegas et al. suggest that this population of dopamine neurons might be particularly relevant to Parkinson's disease and that focusing future studies on them could ultimately be beneficial for patients.

DOI:http://dx.doi.org/10.7554/eLife.10032.002

Profile of changes in bone turnover markers during once-weekly teriparatide administration for 24 weeks in postmenopausal women with osteoporosis

SUMMARY

Changes in bone turnover markers with weekly 56.5 μg teriparatide injections for 24 weeks were investigated in women with osteoporosis. Changes in bone turnover markers 24 h after each injection of teriparatide were constant. During the 24 week period, bone formation markers increased and baseline bone resorption marker levels were maintained.

INTRODUCTION

This study aimed to clarify the changes in bone turnover markers during 24 weeks of once-weekly teriparatide injections in postmenopausal women with osteoporosis.

METHODS

The 24 h changes in pharmacokinetics (PK), calcium metabolism, and bone turnover markers (serum osteocalcin, procollagen type I N-terminal propeptide (P1NP), urinary cross-linked N-telopeptide of type I collagen (NTX), deoxypiridinoline (DPD)) after each injection of 56.5 μg teriparatide at the data collection weeks (0, 4, 12, and 24 weeks) were investigated. The changes were evaluated by comparison with the data at 0 h in each data collection week.

RESULTS

Similar 24 h changes in each parameter after injection of teriparatide were observed in each data collection week. Serum calcium increased transiently, and intact PTH decreased 4-8 h after injection; serum calcium subsequently returned to baseline levels. Calcium and intact PTH levels decreased for 24 weeks. Although serum osteocalcin decreased at 24 h, it was significantly increased at 4 weeks. P1NP decreased transiently and then increased significantly at 24 h. P1NP was significantly increased at 4 weeks. Urinary NTX and DPD were significantly increased transiently and then decreased at 24 h. The urinary DPD level decreased significantly at 4 weeks.

CONCLUSIONS

Twenty-four hour changes in PK, calcium metabolism, and bone turnover markers showed the same direction and level after once-weekly teriparatide injections for 24 weeks, with no attenuation of the effect over time. After 24 weeks, the bone formation marker, serum osteocalcin, increased significantly, but the serum P1NP, did not. Bone resorption markers decreased or remained the same.

Molecular organization of vomeronasal chemoreception

The vomeronasal organ (VNO) has a key role in mediating the social and defensive responses of many terrestrial vertebrates to species- and sex-specific chemosignals. More than 250 putative pheromone receptors have been identified in the mouse VNO, but the nature of the signals detected by individual VNO receptors has not yet been elucidated. To gain insight into the molecular logic of VNO detection leading to mating, aggression or defensive responses, we sought to uncover the response profiles of individual vomeronasal receptors to a wide range of animal cues. Here we describe the repertoire of behaviourally and physiologically relevant stimuli detected by a large number of individual vomeronasal receptors in mice, and define a global map of vomeronasal signal detection. We demonstrate that the two classes (V1R and V2R) of vomeronasal receptors use fundamentally different strategies to encode chemosensory information, and that distinct receptor subfamilies have evolved towards the specific recognition of certain animal groups or chemical structures. The association of large subsets of vomeronasal receptors with cognate, ethologically and physiologically relevant stimuli establishes the molecular foundation of vomeronasal information coding, and opens new avenues for further investigating the neural mechanisms underlying behaviour specificity.

Tertiary structures of gastrin-like tetrapeptides

Tertiary structures of gastrin-like tetrapeptide Trp-Met-Asp-Phe-NH2 and those substituted by Leu, Val or Gly for Met are studied. The lowest energy conformations of the side chains when the back bone is fixed in alpha-helix are obtained by modified minimization algorithm. It is suggested that protein folding proceeds in the accessible conformation space as a self-organization process leading to minimum energy conformation in this space.

Transcription of histone gene cluster by differential core-promoter factors

The 100 copies of tandemly arrayed Drosophila linker (H1) and core (H2A/B and H3/H4) histone gene cluster are coordinately regulated during the cell cycle. However, the molecular mechanisms that must allow differential transcription of linker versus core histones prevalent during development remain elusive. Here, we used fluorescence imaging, biochemistry, and genetics to show that TBP (TATA-box-binding protein)-related factor 2 (TRF2) selectively regulates the TATA-less Histone H1 gene promoter, while TBP/TFIID targets core histone transcription. Importantly, TRF2-depleted polytene chromosomes display severe chromosomal structural defects. This selective usage of TRF2 and TBP provides a novel mechanism to differentially direct transcription within the histone cluster. Moreover, genome-wide chromatin immunoprecipitation (ChIP)-on-chip analyses coupled with RNA interference (RNAi)-mediated functional studies revealed that TRF2 targets several classes of TATA-less promoters of >1000 genes including those driving transcription of essential chromatin organization and protein synthesis genes. Our studies establish that TRF2 promoter recognition complexes play a significantly more central role in governing metazoan transcription than previously appreciated.

Novel TRF1/BRF target genes revealed by genome-wide analysis of Drosophila Pol III transcription

Metazoans have evolved multiple paralogues of the TATA binding protein (TBP), adding another tunable level of gene control at core promoters. While TBP-related factor 1 (TRF1) shares extensive homology with TBP and can direct both Pol II and Pol III transcription in vitro, TRF1 target sites in vivo have remained elusive. Here, we report the genome-wide identification of TRF1-binding sites using high-resolution genome tiling microarrays. We found 354 TRF1-binding sites genome-wide with approximately 78% of these sites displaying colocalization with BRF. Strikingly, the majority of TRF1 target genes are Pol III-dependent small noncoding RNAs such as tRNAs and small nonmessenger RNAs. We provide direct evidence that the TRF1/BRF complex is functionally required for the activity of two novel TRF1 targets (7SL RNA and small nucleolar RNAs). Our studies suggest that unlike most other eukaryotic organisms that rely on TBP for Pol III transcription, in Drosophila and possibly other insects the alternative TRF1/BRF complex appears responsible for the initiation of all known classes of Pol III transcription.

Coactivator cross-talk specifies transcriptional output

Cells often fine-tune gene expression at the level of transcription to generate the appropriate response to a given environmental or developmental stimulus. Both positive and negative influences on gene expression must be balanced to produce the correct level of mRNA synthesis. To this end, the cell uses several classes of regulatory coactivator complexes including two central players, TFIID and Mediator (MED), in potentiating activated transcription. Both of these complexes integrate activator signals and convey them to the basal apparatus. Interestingly, many promoters require both regulatory complexes, although at first glance they may seem to be redundant. Here we have used RNA interference (RNAi) in Drosophila cells to selectively deplete subunits of the MED and TFIID complexes to dissect the contribution of each of these complexes in modulating activated transcription. We exploited the robust response of the metallothionein genes to heavy metal as a model for transcriptional activation by analyzing direct factor recruitment in both heterogeneous cell populations and at the single-cell level. Intriguingly, we find that MED and TFIID interact functionally to modulate transcriptional response to metal. The metal response element-binding transcription factor-1 (MTF-1) recruits TFIID, which then binds promoter DNA, setting up a "checkpoint complex" for the initiation of transcription that is subsequently activated upon recruitment of the MED complex. The appropriate expression level of the endogenous metallothionein genes is achieved only when the activities of these two coactivators are balanced. Surprisingly, we find that the same activator (MTF-1) requires different coactivator subunits depending on the context of the core promoter. Finally, we find that the stability of multi-subunit coactivator complexes can be compromised by loss of a single subunit, underscoring the potential for combinatorial control of transcription activation.

Targeting genes and transcription factors to segregated nuclear compartments

With increasingly detailed images of nuclear structures revealed by advanced microscopy, a remarkably compartmentalized cell nucleus has come into focus. Although this complex nuclear organization remains largely unexplored, some progress has been made in deciphering the functional aspects of various subnuclear structures, revealing how this elaborate framework can influence gene activation. Several recent studies have helped illustrate how cells might utilize the nuclear architecture as an additional level of transcriptional control, perhaps by targeting genes and regulatory factors to specific sites within the nucleus that are designated for active RNA synthesis.

Site-dependent effect of O-glycosylation on the conformation and biological activity of calcitonin

We synthesized seven O-glycosylated calcitonin derivatives, each with a single GalNAc residue attached to either Ser or Thr, and studied their three-dimensional structure and biological activity to examine site-dependent effects of O-glycosylation. The CD spectra in an aqueous trifluoroethanol solution showed that the GalNAc attachment at Thr6 or Thr21 reduced the helical content of calcitonin, indicating that the O-glycosylated residue functions as a stronger helix breaker than the original amino acid residue. Only the GalNAc attachment at Ser2 or Thr21 retained the hypocalcemic activity of calcitonin. This result corresponded well to that of the calcitonin-receptor binding assay. The GalNAc attachment other than Ser2 or Thr21 perturbed the interaction with the receptor, resulting in the loss of the hypocalcemic activity. The biodistribution did not change much among the seven derivatives, but some site dependency could also be observed. Thus, we can conclude that the O-glycosylation affects both the conformation and biological activity in a site-dependent manner.

Knowledge-based potential defined for a rotamer library to design protein sequences

A knowledge-based potential for a rotamer library was developed to design protein sequences. Protein side-chain conformations are represented by 56 templates. Each of their fitness to a given structural site-environment is evaluated by a combined function of the three knowledge-based terms, i.e. two-body side-chain packing, one-body hydration and local conformation. The number of matches between the native sequence and the structural site-environment in the database and that of the virtually settled mismatches, counted in advance, were transformed into the energy scores. In the best-14 test (assessment for the reproduction ability of the native rotamer on its structural site within a quarter of 56 fitness rank positions), the structural stability analysis on mutants of human and T4 lysozymes and the inverse-folding search by a structure profile against the sequence database, this function performs better than the function deduced with the conventional normalization and our previously developed function. Targeting various structural motifs, de novo sequence design was conducted with the function. The sequences thus obtained exhibit reasonable molecular masses and hydrophobic/hydrophilic patterns similar to the native sequences of the target and act as if they were the homologs to the target proteins in BLASTP search. This significant improvement is discussed in terms of the reference state for normalization and the crucial role of short-range repulsion to prohibit residue bumps.

Effect of carbohydrate structure on biological activity of artificially N-glycosylated eel calcitonin

To reveal the function of the carbohydrate portion of glycopeptides and glycoproteins, we chemo-enzymatically synthesized artificially N-glycosylated derivatives of eel calcitonin and studied their three-dimensional structure and biological activity. The CD and NMR spectra in trifluoroethanol-H(2)O solution showed that the glycosylation did not change the three-dimensional structure. All the derivatives retained the strong in vivo hypocalcemic activity of calcitonin. However, the relative activity was dependent on the structure of the attached carbohydrate. The single GlcNAc attachment best enhanced the activity, while larger carbohydrates decreased the activity. This relative activity order of compounds could be partly explained by their calcitonin-receptor binding affinity, though the affinity of the GlcNAc derivative did not exceed that of calcitonin. The enhanced hypocalcemic activity of the GlcNAc derivative was explained by its altered biodistribution. The GlcNAc attachment caused calcitonin to escape from the trap at the liver during the early circulation. Thus, the glycosylation was shown to modulate the biological activity of calcitonin depending on the carbohydrate structure without a change in the peptide backbone conformation.

Structure of cytochrome c6 from the red alga Porphyra yezoensis at 1. 57 A resolution

The crystal structure of cytochrome c(6) from the red alga Porphyra yezoensis has been determined at 1.57 A resolution. The crystal is tetragonal and belongs to space group P4(3)2(1)2, with unit-cell parameters a = b = 49.26 (3), c = 83.45 (4) A and one molecule per asymmetric unit. The structure was solved by the molecular-replacement method and refined with X-PLOR to an R factor of 19.9% and a free R factor of 25.4%. The overall structure of cytochrome c(6) follows the topology of class I c-type cytochromes in which the heme prosthetic group covalently binds to Cys14 and Cys17, and the iron has an octahedral coordination with His18 and Met58 as the axial ligands. The sequence and the structure of the eukaryotic red algal cytochrome c(6) are very similar to those of a prokaryotic cyanobacterial cytochrome c(6) rather than those of eukaryotic green algal c(6) cytochromes.

Self-assembly of heme A and heme B in a designed four-helix bundle: implications for a cytochrome c oxidase maquette

Heme A, a prosthetic group of cytochrome c oxidase [EC 1.9.3.1], has been introduced into two de novo designed four helix bundle proteins, [H10A24](2) and [H10H24](2), known to bind 2-4 equiv of heme B, respectively [Robertson, D. E., Farid, R. S., Moser, C. C., Mulholland, S. E., Pidikiti, R., Lear, J. D., Wand, A., J., DeGrado, W. F., and Dutton, P. L. (1994) Nature 368, 425-432]. [H10A24](2), [Ac-CGGGELWKL x HEELLKK x FEELLKL x AEERLKK x L-CONH(2)](2)(2), binds two heme A molecules per four-helix unit via bis-histidine ligation at the 10,10' positions with measured K(d) values of <0.1 and 5 nM, values much lower than those measured for heme B (K(d) values of 50 and 800 nM). The heme A-protein complex, [heme A-H10A24](2), exhibits well-defined absorption spectra in both the ferric and ferrous states, and an electron paramagnetic resonance spectrum characteristic of a low spin heme in the ferric form. A single midpoint redox potential (E(m8)) was determined for [heme A-H10A24](2) at -45 mV (vs SHE), which is significantly higher than that of the protein bound heme B (-130 and -200 mV). The observation of a single midpoint redox potential for [heme A-H10A24](2) and a pair of midpoints for [heme B-H10A24](2) indicates that the di-alpha-helical monomers are oriented in an anti topology (disulfides on opposite sides of bundle) in the former (lacking heme-heme electrostatic interaction) and syn in the latter. A mixture of global topologies was indicated by the potentiometric titration of the related [heme A-H10H24](2) which possess two distinct reduction potentials of +41 (31%) and -65 mV (69%). Self-assembly of the mixed cofactor heme A-heme B-[H10A24](2) was accomplished by addition of a single equivalent of each heme A and heme B to [H10A24](2). The single midpoint redox potential of heme B, E(m8) = -200 mV, together with the split midpoint redox potential of heme A in heme A-heme B-[H10A24](2), E(m8) = +28 mV (33%) and -65 mV (67%), indicated the existence of both syn and anti topologies of the two di-alpha-helical monomers in this four helix bundle. Synthesis of the mixed cofactor [heme A-heme B-H10H24](2) was accomplished by addition of a 2 equiv of each heme A and heme B to [H10H24](2) and potentiometry indicated the pair of hemes B resided in the 10,10' sites and heme A occupied the 24,24' sites. The results indicate that heme peripheral structure controls the orientation of the di-alpha-helical monomers in the four-helix bundle which are interchangeable between syn and anti topologies. In the reduced form, [heme A-H10A24](2), reacts quantitatively to form [carbonmonoxy-heme A-H10A24](2) as evidenced by optical spectroscopy. The synthetic [heme A-H10A24](2) can be enzymatically reduced by NAD(P)H with natural reductases under anaerobic conditions, and reversibly oxidized by dioxygen to the ferric form.

Expression, purification, and characterization of blasticidin S deaminase (BSD) from Aspergillus terreus: the role of catalytic zinc in enzyme structure

We established an efficient overproduction-purification system for blasticidin S deaminase (BSD) using the cDNA cloned from Aspergillus terreus. The estimated molecular mass of the purified enzyme indicated BSD was a tetramer. This tetrameric form was very resistant to denaturation by SDS and showed heat-modifiable behavior on SDS-PAGE; i.e., BSD migrated much slower (as a single band of 36 kDa) in its active conformation than its completely denatured polypeptide (13 kDa) if heat treatment in 2% SDS was not performed before electrophoresis. As predicted from the presence of the catalytic zinc-coordinating sequence motif conserved in the cytosine nucleoside/nucleotide deaminase family, BSD also contained one zinc per deaminase subunit. However, the predicted catalytic function appeared not to be the only role of this zinc in the enzyme. First, titration of the zinc-chelating -SH groups with p-hydroxymercuriphenylsulfonate led to dissociation of the BSD tetramer into unstable monomers or dimers. Second, depletion of zinc on reconstitution of chemically denatured BSD (with either guanidine-HCl or acidic pH) resulted in improper folding of the polypeptide. These results suggest that zinc also plays a structural role in maintenance of the protein structure. When we introduced mutations at Glu-56 (the proposed active site) and Cys-91 (a proposed catalytic zinc-binding Cys) in BSD, none of the resulting mutants (E56D, E56Q, C91A, C91S, and C91H) showed any detectable activity, as judged with the spectrophotometric assay. Replacements of Cys-91 resulted in gross perturbation of the enzyme structure although the catalytically essential Glu-56 was not necessarily required for proper folding of the enzyme. These results further support our proposal that the catalytic zinc coordinated by the conserved sequence motif is also structural in BSD.

Redesign of artificial globins: effects of residue replacements at hydrophobic sites on the structural properties

Artificial sequences of the 153 amino acids have been designed to fit the main-chain framework of the sperm whale myoglobin (Mb) structure based on a knowledge-based 3D-1D compatibility method. The previously designed artificial globin (DG1) folded into a monomeric, compact, highly helical and globular form with overall dimensions similar to those of the target structure, but it lacked structural uniqueness at the side-chain level [Isogai, Y., Ota, M., Fujisawa, T. , Izuno, H., Mukai, M., Nakamura, H., Iizuka, T., and Nishikawa, K. (1999) Biochemistry 38, 7431-7443]. In this study, we redesigned hydrophobic sites of DG1 to improve the structural specificity. Several Leu and Met residues in DG1 were replaced with beta-branched amino acids, Ile and Val, referring to the 3D profile of DG1 to produce three redesigned globins, DG2-4. These residue replacements resulted in no significant changes of their compactness and alpha-helical contents in the absence of denaturant, whereas they significantly affected the dependence of the secondary structure on the concentration of guanidine hydrochloride. The analyses of the denaturation curves revealed higher global stabilities of the designed globins than that of natural apoMb. Among DG1-4, DG3, in which 11 Leu residues of DG1 are replaced with seven Ile and four Val residues, and one Met residue is replaced with Val, displayed the lowest stability but the most cooperative folding-unfolding transition and the most dispersed NMR spectrum with the smallest line width. The present results indicate that the replacements of Leu (Met) with the beta-branched amino acids at appropriate sites reduce the freedom of side-chain conformation and improve the structural specificity at the expense of stability.

Characterization and amino acid sequences of cytochromes c6 from two strains of the green alga Chlorella vulgaris

Cytochromes c6 from the green algae Chlorella vulgaris CK-5 (CK5cyc6) and C. vulgaris CK-22 (CK22cyc6) were characterized and their amino acid sequences were analyzed. CK5cyc6 had a molecular mass of 9.3 kDa, isoelectric points of 3.0 (reduced) and 3.6 (oxidized), and a redox potential of +362 mV at pH 7.0. CK22cyc6 had a molecular mass of 9.5 kDa, isoelectric points of 2.9 (reduced) and 3.5 (oxidized), and a redox potential of +355 mV at pH 7.0. The absorption spectra of both cytochromes c6 showed 4 maxima in reduced form, and 2 maxima and a weak peak at 695 nm in oxidized form. The pyridine ferrohemochrome spectra indicated that their prosthetic group was heme c. These physicochemical properties were similar to those of other algal cytochromes c6. The amino acids (88 residues) of CK5cyc6 and CK22cyc6 were sequenced and the sequence motif -CXXCH-, which is typical of the heme-binding site of c-type cytochrome, was clearly confirmed in both cytochromes. Twenty-six amino acid residues were substituted, and the similarity score of each of them was 70.45%.

Rat epididymal sperm motion changes induced by ethylene glycol monoethyl ether, sulfasalazine, and 2,5-hexandione

Epididymal sperm was examined using the Hamilton-Thorne Sperm analyzer (HTM-IVOS, version 10.6) in male rats treated with known male reproductive toxicants that act by different mechanisms to detect effects on sperm motion. Three agents known to produce changes in sperm motion at high exposure levels were administered at lower levels. Ethylene glycol monoethyl ether (EGEE), sulfasalazine (SASP), and 2,5-hexandione (2,5-HD) were administered by oral gavage to adult male Sprague-Dawley rats at 250 or 500 mg/kg/day, at 300 or 600 mg/kg/day, or at 100 or 250 mg/kg/day, respectively. The males were treated with EGEE, SASP, and 2,5-HD for 35, 28, and 28 days, respectively. The males treated with EGEE and SASP were mated with untreated females to assess male fertility. All males were examined for body weight, testicular and epididymal weight, epididymal sperm count, and sperm motion. The sperm motion parameters included percentage of motile sperm, percentage of progressively motile sperm (progressive motility), curvilinear velocity (VCL), average path velocity (VAP), straight line velocity (VSL), amplitude of lateral head displacement (ALH), beat cross frequency (BCF), linearity (LIN), and straightness (STR). For the male rats treated with SASP, no treatment-related effects on percentages of motile sperm or sperm count were observed despite impaired male fertility. However, abnormal motion of epididymal sperm from the SASP treated males was detected by a significant reduction in mean progressive motility, VAP, and ALH, and an increase in BCF and STR. For the males treated with 2,5-HD for 4 weeks, most parameters generated by the HTM-IVOS indicated decreased sperm motion despite no remarkable changes in testicular weight, epididymal weight, or sperm count. In the EGEE-treated males at 250 mg/kg/day for 5 weeks, abnormal motion of epididymal sperm was detected by decreased progressive motility and increased BCF, although there were no treatment-related effects on testicular weight or male fertility. Progressive motility was decreased in all treated groups and the difference from the control value was of the greatest magnitude among the sperm motion parameters generated by the HTM-IVOS. Velocity parameters (VAP, VSL, VCL) responded sensitively to abnormal sperm motion in the SASP and 2,5-HD studies. In spite of decreased sperm motion, BCF values were significantly increased in all treated groups except the 7-week EGEE high-dose group, where there were no motile sperm to evaluate. ALH was significantly decreased in the treated groups in which remarkable effects on sperm motion were noted. There were no significant changes in ALH at the low-dose of EGEE at which only mild effects on sperm motion were observed. STR was increased for epididymal sperm from the males treated with SASP when compared with the controls. For the males treated with EGEE and 2,5-HD, however, STR was decreased when compared with the controls. There were no significant differences in LIN in any of the groups treated with SASP, in which remarkably reduced sperm motion was detected by the other parameters. In conclusion, among the parameters generated by the HTM-IVOS, progressive motility was significantly decreased in all treated groups and the most valuable for detecting slight changes in sperm motion induced by these three different target toxicants. Further investigation with a larger set of compounds is needed to evaluate which IVOS parameters are the most sensitive in detecting motion changes.

Design and synthesis of a globin fold

We propose a simple method to find an amino acid sequence that is foldable into a globular protein with a desired structure based on a knowledge-based 3D-1D compatibility function. An asymmetric alpha-helical single-domain structure of sperm whale myoglobin consisting of 153 amino acid residues was chosen for the design target. The optimal sequence to fit the main-chain framework has been searched by recursive generation of the protein 3D profile. The heme-binding site was designed by fixing His64 and His93 at the distal and proximal positions, respectively, and by penalizing residues that protrude into the space with a repulsive function. The apparent bumps among side chains in the computer model of the converged, self-consistent sequence were removed by replacing some of the bumping residues with smaller ones according to the final 3D profile. The finally obtained sequence shares 26% of sequence with the natural myoglobin. The designed globin-1 (DG1) with the artificial sequence was obtained by expression of the synthetic gene in Escherichia coli. Analyses using size-exclusion chromatography, circular dichroism spectroscopy, and solution X-ray scattering showed that DG1 folds into a monomeric, compact, highly helical, and globular form with an overall molecular shape similar to the target structure in an aqueous solution. Furthermore, it binds a single heme per protein molecule, which exhibited well-defined spectroscopic properties. The radius of gyration of DG1 was determined to be 20.6 A, slightly larger than that of natural apoMb, and decreased to 19.5 A upon heme binding based on X-ray scattering analysis. However, the heme-bound DG1 did not stably bind molecular oxygen as natural globins do, possibly due to high conformational diversity of side-chain structures observed in the NMR and denaturation experiments. These results give insight into the relationship between the sequence selection and the structural uniqueness of natural proteins to achieve biological functions.

Matrix-assisted laser desorption ionization mass spectrometry for the analysis of monosulfated oligosaccharides

Sulfated oligosaccharides are an important class of compounds in the field of glycobiology. Mass spectrometric analysis of these molecules is challenging due to their readiness to dissociate in sample preparation and their tendency to fragment during ionization. Moreover, their presence in small quantity in biological systems poses additional problems. We report the development of a mass spectrometric method based on matrix-assisted laser desorption ionization (MALDI) in a time-lag focusing time-of-flight mass spectrometer for the analysis of monosulfated oligosaccharides. It is found that coumarin 120 is an excellent matrix for the analysis of monosulfated disaccharides, whereas the use of a mixture of coumarin 120 and 6-aza-2-thiothymine is very effective for the ionization of sulfated trisaccharides and tetrasaccharides including those containing N-acetylneuraminic acid. Molecular ions for a series of synthetic sulfo/sialo beta Gal(1-->3)GlcNAc and beta Gal(1-->4)GlcNAc structures can thus be observed with subpicomole detection sensitivity using a uniform microcrystal matrix/sample preparation procedure. It is demonstrated that, with this matrix formulation, the presence of a high amount of sodium chloride or sodium phosphate buffer, which is often the case for the HPLC fractionated samples, does not deteriorate the MALDI performance. The analysis of mixtures containing different types of oligosaccharides is also examined. It is found that different classes of oligosaccharides require different matrix preparation methods.

Structural requirement of highly-conserved residues in globins

Globins have remarkable sequence diversity, and yet maintain a common fold. In spite of the diversity, there are highly-conserved residues at several sites. The conserved residues were examined in terms of the structural stability, by employing the pseudo-energy functions of the structure/sequence compatibility method. The fitness of each residue type to the structural environment was evaluated at seven highly-conserved sites: the Leu (at the B10 site), Phe (CD1), and Leu (F4) residues were found to fit their respective sites due to hydrophobic interactions; Pro (C2) stabilizes the N-terminal edge of an alpha-helical structure; and Phe (CD4) is stabilized by backbone hydrogen-bonding to Phe (CD1). On the other hand, the other two residues, His (E7) and His (F8), are poorly suited to the sites from a structural viewpoint, suggesting that their conservation clearly results from a heme-related functional requirement. The invariant Phe residue (CD1) has been suggested to be important for supporting the heme. The present analysis revealed that this residue is also well suited to the site in terms of energy.

Mechanisms of nitroso compound-induced inhibition of superoxide generation in neutrophils: fluorescence quenching of perylene by nitroso-compounds in the membrane fractions of neutrophils

To investigate the mechanism of nitroso compound-induced inhibition of the respiratory burst in neutrophils, we studied fluorescence quenching of perylene by nitroso-compounds in the membrane fractions of neutrophils at 17, 27, and 37 degrees C and the reagent-induced inhibition of superoxide generation at 28 and 37 degrees C. With increasing temperature, the quenching of perylene fluorescence and inhibition of superoxide generation by nitrosobenzene (NB) were both diminished, while those by 2-nitrosotoluene (NT) were both enhanced. The temperature dependence of the inhibition constants and the quenching constants indicates that the binding of NB is exothermic (deltaH= -27 kJ/mol for inhibition and deltaH= -29 kJ/mol for quenching) and essentially enthalpy-driven. On the other hand, that of NT is endothermic (deltaH= +16 kJ/mol for inhibition and quenching) and essentially entropy-driven. Quenching studies of perylene fluorescence in synthetic vesicles made of endogenous polar lipids of neutrophils showed that the enthalpy changes of NB- and NT-binding with perylene in lipids were similar to each other. Moreover, their values were in good agreement with that of NT, but not of NB, in the membrane fractions, an assembly of proteins and lipids, of neutrophils. These results suggest that NB inhibits the activity by binding to proteins in the membrane, whereas inhibition by NT occurs through hydrophobic interaction with lipids and/or proteins.

Rheological study of the dynamic process of fibrinolysis

The dynamic process of fibrinolysis induced by tissue plasminogen activator was examined using a rheological technique. Change in a rheological parameter (logarithmic damping factor) of whole blood and platelet-free plasma during fibrinolysis was largely dependent on the initial concentration of tissue plasminogen activator. Addition of activated partial prothrombin time reagent allowed determination of the time both of onset and end of fibrinolysis without affecting the coagulation process. The changes in the clot structure of fibrin during fibrinolysis were observed with a scanning electron microscope and compared with the time-dependent behavior of the logarithmic damping factor. Differences in the logarithmic damping factor during fibrinolysis were evident in alteration of the network structure of clots. It will be shown that the present rheological technique is useful for examining the concentration dependence of fibrinolytic reagent on fibrinolysis as well as for monitoring the dynamic process of fibrinolysis.

Effect of aromatic nitroso-compounds on superoxide-generating activity in neutrophils

Aromatic nitroso-compounds such as nitrosobenzene inhibited the respiratory burst of intact neutrophils induced by various stimulants, including phorbol 12-myristate 13-acetate and a chemotactic peptide. The compounds also inhibited NADPH-dependent oxygen consumption by cell-free preparations of neutrophils. This indicates that nitroso-compounds act directly on the NADPH-oxidase system. The inhibitory effects induced by several nitroso-compounds, 2-nitrosotoluene, nitrosobenzene, 4-nitrosophenol, and 1-nitrosopyrrolidine, were examined and their inhibition constants, the concentrations causing 50% reduction of oxygen consumption, were found to be 0.043, 0.173, 0.672, and 32.1 mM, respectively. These values correlated well with the hydrophobicity of the compounds: a more hydrophobic compound was a more potent inhibitor against NADPH oxidase, suggesting that the oxidase has a hydrophobic site(s) for interaction with the inhibitors.

Calcitonin-induced changes in the cytoskeleton are mediated by a signal pathway associated with protein kinase A in osteoclasts

Calcitonin is known to inhibit osteoclastic bone resorption through its receptor, which is abundantly expressed on the plasma membrane of osteoclasts. Recently, it was reported that calcitonin receptors were coupled to both cAMP-dependent protein kinase (PKA) and protein kinase C (PKC). To examine how the PKA and PKC pathways are involved in the effects of calcitonin, we focused on changes in the cytoskeleton of murine osteoclast-like multinucleated cells (OCLs) formed in vitro. When OCLs were cultured on dentine slices, they formed resorption pits and ringed structures of F-actin dots (actin rings). Elcatonin, a synthetic analogue of eel calcitonin, disrupted actin rings and inhibited pit formation in a dose-dependent manner. Forskolin and dibutyryl cAMP, both of which have the ability to activate PKA, mimicked the effects of elcatonin. Phorbol myristate acetate and phorbol 12,13-dibutyrate, both of which have the ability to activate PKC, also inhibited pit-forming activity, but little affected actin rings of OCLs. The inhibitory effects of elcatonin on the pit formation and actin ring formation were partially restored by the treatment with Rp-cAMPs, a cAMP antagonist. Elcatonin induced a rapid increase in PKA activity within a few minutes, and its activation by elcatonin occurred in a dose-dependent manner. The time- and dose-dependent profiles of elcatonin for the activation of PKA were similar to those for the disruption of actin rings. Moreover, microinjection of activated PKA into OCLs disrupted actin rings within 10 min on culture dishes. Actin rings were little affected by the microinjection of the PKA preincubated with a cAMP-dependent protein kinase inhibitor (IP-20) into OCLs. These results suggest that PKA activation, rather than PKC activation, is involved in mediating the effects of calcitonin, through the disruption of actin organization.

6'-Sulfo sialyl Lex but not 6-sulfo sialyl Lex expressed on the cell surface supports L-selectin-mediated adhesion

In order to determine if a sulfated oligosaccharide on the cell surface can function as an L-selectin ligand, a novel approach for in vitro transfer of oligosaccharides was utilized (Srivastava, G., Kaun, K. J., Hindsgaul, O., and Palcic, M. M. (1992) J. Biol. Chem. 267, 22356-22361). CHO cells were incubated with synthetic 6'-sulfo sialyl Lex, NeuNAcalpha2-->3(sulfate-6)Galbeta1-->4(Fucalpha1-->3) GlcNAc or 6-sulfo sialyl Lex, NeuNAcalpha2-->3Galbeta1-->4[(Fucalpha1-->3)sulfate--> 6GlcNAc] oligosaccharide linked to C-6 of a fucose residue in GDP-fucose and a milk fucosyltransferase. The resultant CHO cells expressing 6'-sulfo sialyl Lex or 6-sulfo sialyl Lex on their cell surface were tested for adhesion to E-selectin and L-selectin chimeric proteins coated on plates. The results indicate that 6'-sulfo sialyl Lex supports L-selectin-mediated adhesion much better than sialyl Lex similarly tagged on the cell surface. In contrast, 6-sulfo sialyl Lex containing a sulfate group on the N-acetylglucosamine residue did not support adhesion with either selectin. These combined results suggest that 6'-sulfo sialyl Lex is a much better ligand than sialyl Lex oligosaccharide for L-selectin.

Parathyroid hormone regulates osteoblast differentiation positively or negatively depending on the differentiation stages

The effects of parathyroid hormone (1-34) (PTH (1-34) on osteoblast differentiation were investigated using primary osteoblast-like cells isolated from newborn mouse calvaria. The osteoblast-like cells cultured at low cell densities, in which the cells remained in a subconfluent state at the end of culture, were exposed for 7 days to PTH. This stimulated alkaline phosphatase (ALP) activity in a dose-dependent manner. In contrast, PTH dose-dependently inhibited both ALP activity and osteocalcin production in cells inoculated at high cell densities, in which they had reached a confluent state before the end of culture. The changes of ALP activity by PTH were accompanied with the expression of ALP messenger RNA. PTH induced no changes of the hydroxyproline content in the cell layer when the cells were exposed to the hormone at a subconfluent state, but reduced the content at a postconfluent state. The stimulation of ALP activity by PTH at a preconfluent state was retained even after the removal of PTH from the culture media. The opposite effect of PTH, observed between the preconfluent and the postconfluent state, was reproduced by adding dibutyryl cyclic adenosine monophosphate (cAMP) or forskolin, but not by adding phorbol myristate acetate. In a colony-forming unit fibroblastic (CFU-F) assay, using bone marrow cells isolated from tibiae of 10-week-old mice, PTH induced no changes in the total number of CFU-Fs, but increased the proportion of ALP-positive colonies. These results indicate that PTH exerts opposite effects on the phenotypic expression of osteoblasts, depending on their differentiation stages of osteoblasts. PTH may preferentially stimulate osteoblast differentiation in immature osteoblasts but inhibit it in more mature cells.

The alpha(1,3)fucosyltransferase Fuc-TVII controls leukocyte trafficking through an essential role in L-, E-, and P-selectin ligand biosynthesis

alpha(1,3)Fucosylated oligosaccharides represent components of leukocyte counterreceptors for E- and P-selectins and of L-selectin ligands expressed by lymph node high endothelial venules (HEV). The identity of the alpha(1,3)fucosyltransferase(s) required for their expression has been uncertain, as has a requirement for alpha(1,3)fucosylation in HEV L-selectin ligand activity. We demonstrate here that mice deficient in alpha(1,3) fucosyltransferase Fuc-TVII exhibit a leukocyte adhesion deficiency characterized by absent leukocyte E- and P-selectin ligand activity and deficient HEV L-selectin ligand activity. Selectin ligand deficiency is distinguished by blood leukocytosis, impaired leukocyte extravasation in inflammation, and faulty lymphocyte homing. These observations demonstrate an essential role for Fuc-TVII in E-, P-, and L-selectin ligand biosynthesis and imply that this locus can control leukocyte trafficking in health and disease.

Direct measurement of oscillatory generation of superoxide anions by single phagocytes

Phagocytic cells such as neutrophils generate superoxide anions (O2-) within phagocytic vacuoles for killing and digesting microorganisms. Here we report the simultaneous observation of morphological changes and O2- generation in single phagocytic cells during phagocytosis. Point stimulation of a cell by contact with an opsonized microelectrode at the cell surface induced significant deformation to engulf the electrode, and also induced the O2- generation which was measured by the electrode. Periodic fluctuations in the magnitude of the O2- generation were observed in the time course. These oscillations may be caused by metabolic regulation of the formation of NADPH, which is the substrate for the O2- generation

Resolution of the aerobic respiratory system of the thermoacidophilic archaeon, Sulfolobus sp. strain 7. II. Characterization of the archaeal terminal oxidase subcomplexes and implication for the intramolecular electron transfer

The terminal segment of the aerobic respiratory chain of the thermoacidophilic archaeon Sulfolobus sp. strain 7 is an unusual caldariellaquinol oxidase supercomplex, which contains at least one b-type and three spectroscopically distinguishable a-type cytochromes, one copper, and a Rieske-type FeS center. In this paper, we report the purification and characterization of two different forms of the archaeal a-type cytochromes, namely, a three-subunit cytochrome a583-aa3 subcomplex and a single-subunit cytochrome aa3 derived from the cytochrome subcomplex, in order to facilitate further studies on the terminal oxidase segment of Sulfolobus. The optical and EPR spectroscopic analyses suggest the presence of two different low-spin heme centers and one high-spin heme center in the purified cytochrome a583-aa3 subcomplex, and one low-spin and one high-spin hemes in cytochrome aa3, respectively. The Rieske-type FeS center detected in the purified cytochrome supercomplex was absent in two forms of the a-type cytochrome oxidase, indicating its association with cytochrome b562. The crystal field parameters of the lowspin heme a583 center indicate that its axial ligands may be similar to those of cytochromes c, rather than conventional bis-histidine ligation. In spite of the absence of any c-type cytochrome, a ferrocytochrome c oxidase activity was detected in the archaeal purified cytochrome a583-aa3 subcomplex with no quinol oxidase activity, but not in the purified cytochrome oxidase supercomplex, which has been tentatively interpreted as a representative of electron transfer from the Rieske FeS center to cytochrome a583 in vivo. Thus, our results indicate the following scheme for the intramolecular electron transfer of the terminal oxidase supercomplex from Sulfolobus sp. strain 7: [caldariellaquinol-->] b562-->Rieske FeS center-->a583 aa3-->molecular oxygen.

Changes in auditory P300 event-related potentials and brainstem evoked potentials in diabetes mellitus

To investigate the influence of diabetes mellitus on higher cognitive functions electrophysiologically, we studied auditory P300 event-related potentials (P300) in 40 NIDDM patients, taking into account wave I-V latencies (I-V) in auditory brainstem evoked potentials, clinical parameters and head MRI findings. Compared with 20 controls, diabetics had significantly longer P300 and I-V latencies. P300 latencies in diabetics correlated with neither I-V, HbA1, blood glucose levels, nor disease duration. Of the 13 diabetics investigated neuroradiologically, four had lacunar infarcts with prolonged electrophysiological values. The remaining nine had normal MRI scans, but their physiological parameters were still significantly longer than those of controls. These findings suggest that NIDDM can independently alter higher cognitive and the central auditory pathway functions. Our data also suggest that these alterations occur regardless of the recent metabolic derangement and disease duration. Cerebrovascular ischemia, if present, also appears to contribute in part to cognitive alterations.

The effect of macrophage colony-stimulating factor (M-CSF) on the progression of lipid-induced nephrotoxicity in diabetic nephropathy

In order to elucidate the role of macrophage in lipid-induced nephrotoxicity in diabetic nephropathy, we examined the effect of macrophage colony-stimulating factor (M-CSF) on the progression of renal lesions in hypercholesterolemic steptozotocin (STZ)-diabetic rats fed with high cholesterol chow. Hypercholesterolemia aggravated albuminuria in diabetic rats accompanied by infiltration of macrophages in glomeruli. Treatment with M-CSF suppressed simultaneously infiltration of glomerular macrophages and urinary albumin excretion in hypercholesterolemic diabetic rats. These results suggest that infiltration of glomerular macrophage has a primary role in lipid-induced nephrotoxicity in diabetic nephropathy, and M-CSF is involved in this process as a preventive factor.

Iron-ligand structure and iron redox property of nitric oxide reductase cytochrome P450nor from Fusarium oxysporum: relevance to its NO reduction activity

We studied the nitric oxide reductase, cytochrome P450nor, purified from a denitrifying fungus Fusarium oxysporum with electron paramagnetic resonance spectral and redox potential measurements. The EPR spectral features of P450nor in the ferric resting, the ferric cyanide-bound, and the ferrous NO-bound forms were the same as the corresponding ones of other general P450s such as Pseudomonas putida P450cam. In contrast, the metyrapone complex of ferric P450nor gave an EPR spectrum with significantly different g values from that of P450cam. The EPR results were explained in terms of similarity in the immediate configuration of the S(-)-Fe-ligand (H2O, CN-, NO) structure between P450nor and P450cam but a structural difference at the heme distal pocket, especially in the substrate binding domain; P450cam has a camphor binding domain, while P450nor does not. In spite of the same S(-)-Fe-H2O configuration, the redox potential of P450nor in the ferric/ferrous couple was measured to be -307 mV, which is much lower than those of the camphor-bound (-140 mV) and -free (-250 mV) P450cam. The lower redox potential could be attributable to the different electrostatic interaction of the heme with its surroundings; e.g., the heme environment of P450nor is charged either more negatively or less positively than P450cam.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulredoxin: a novel iron-sulfur protein of the thermoacidophilic archaeon Sulfolobus sp. strain 7 with a Rieske-type [2Fe-2S] center

A novel pink [2Fe-2S] protein has been purified from the cytosol fraction of the thermoacidophilic archaeon Sulfolobus sp. strain 7 (originally named Sulfolobus acidocaldarius 7) and called "sulredoxin." Its absorption, circular dichroism, and electron paramagnetic resonance spectra suggest the presence of a Rieske-type [2Fe-2S] cluster (g-factors of 2.01, 1.91, and 1.79; average g-factor [gav] = 1.90) which is remarkably similar to that of Thermus thermophilus respiratory Rieske FeS protein (J. A. Fee, K. L. Findling, T. Yoshida, R. Hille, G. E. Tarr, D. O. Hearshen, W. R. Dunham, E. P. Day, T. A. Kent, and E. Münck, J. Biol. Chem. 259:124-133, 1984) and distinctively different from those of the plant-type ferredoxins (gav = 1.96). Sulredoxin, which is the first Rieske-type [2Fe-2S] protein isolated from an archaeal species, does not function as an electron acceptor of the cognate 2-oxoacid:ferredoxin oxidoreductase. Whether sulredoxin is derived from the archaeal membrane-bound respiratory Rieske-type FeS center (gy = 1.91) is the subject of further investigation.

Spectral analyses of R-R interval and systolic blood pressure in diabetic autonomic neuropathy

We studied autonomic nervous system function using the principle of maximum entropy (ME) to perform spectral analyses of the R-R interval and systolic blood pressure in 32 diabetic patients and 40 healthy controls. The R-R interval and systolic blood pressure were measured using a continuous, noninvasive monitoring system. The power spectra of both the R-R interval (RR) and systolic blood pressure (SYS) were obtained using ME and the areas of two frequency components were measured: a low- (LFC) and a high-frequency component (HFC). The RR-LFC, RR-HFC and SYS-LFC of diabetic patients were significantly smaller than those of healthy controls. The results of the spectral analyses in diabetic patients correlated with neither disease duration nor nephropathy, while the SYS-LFC showed significant correlations with both retinopathy and the delay in median motor nerve conduction velocity. In the mild autonomic neuropathy group, the RR-LFC and SYS-LFC were not differ from those of healthy controls or patients without autonomic neuropathy. However, the RR-HFC was significantly smaller than that of healthy controls or patients without atonomic neuropathy. In the setting of mild diabetic autonomic neuropathy, it was suggested that cardiac parasympathetic dysfunction preceded both alpha and beta sympathetic dysfunction.

The mechanism of electron donation to molecular oxygen by phagocytic cytochrome b558

Phagocytic cytochrome b558 is a unique heme-containing enzyme, which catalyzes one electron reduction of molecular oxygen to produce a superoxide anion with a six-coordinated heme iron. To clarify the mechanism of the superoxide production, we have analyzed oxidation-reduction kinetics of cytochrome b558 purified from porcine neutrophils by stopped-flow and rapid-scanning spectroscopy. Reduced cytochrome b558 was rapidly reoxidized by O2 showing spectral changes with clear isosbestic points, which were also observed during the reduction of ferric cytochrome b558 with Na2S2O4 under anaerobic conditions. The single turnover rate for the reaction with O2 linearly depended on the O2 concentration but was not affected by addition of CO. The rate of the reaction decreased with an increase of pH giving a pKa of 9.7. Under complete anaerobic conditions, ferrous cytochrome b558 was oxidized by ferricyanide at a rate faster than by O2. The thermodynamic analysis shows that the enthalpic energy barriers for the reactions of cytochrome b558 are significantly lower when compared to the autoxidation of native and modified myoglobins through the formation of the iron-O2 complex. These findings are most consistent with the electron transfer from the heme to O2 by an outer-sphere mechanism.

[Hypocalcemic effect of elcatonin in mouse models for humoral hypercalcemia of malignancy]

To elucidate the effect of calcitonin on humoral hypercalcemia of malignancy (HHM), we studied the effect of elcatonin, a synthetic eel calcitonin analog, on plasma calcium concentration in hypercalcemic nude mice transplanted subcutaneously with FA-6 pancreas cancer cells and hypercalcemic mice produced by continuous infusion of parathyroid hormone-related peptide (PTHrP). Elcatonin proved to exert a potent hypocalcemic effect in either model for hypercalcemia. The effect reached peaks at 2 hr after its administration, and it was no longer detected at 24 hr. The dose-dependent effects of a single administration of elcatonin were studied in the FA-6 tumor-bearing mice: the hypocalcemic effect of elcatonin at 1-2 hr after administration was dose-relatedly augmented. The effect of daily administration of elcatonin was further studied in the FA-6 tumor-bearing mice: 5-Day daily administration of elcatonin was not accompanied by reduction in its hypocalcemic effect. Moreover, it was suggested that higher the efficacy of elcatonin, the higher were the plasma calcium concentrations in the tumor-bearing mice. These results indicated that elcatonin exerts an immediate hypocalcemic effect even on models for acute and severe hypercalcemia such as FA-6 tumor-bearing mice, that this hypocalcemic effect became more potent depending on their elevation of plasma calcium concentration, and that elcatonin exerts a hypocalcemic effect even on a model for hypercalcemia due to PTHrP, a presumable causative substance of HHM.