The nature of the acid-volatile selenium in the liver of the male rat

1. The properties of rat liver acid-volatile selenium have been compared with those of H(2)Se and (CH(3))(2)Se. 2. In model experiments oxidation-sensitive H(2) (75)Se was trapped quantitatively under anaerobic conditions in 0.1m-AgNO(3), and (CH(3))(2) (75)Se was trapped quantitatively in 8m-HNO(3). The acid-labile selenium of a liver homogenate, and of a microsomal fraction, was found to behave quite unlike (CH(3))(2) (75)Se and in a manner indistinguishable from H(2) (75)Se. 3. It was concluded that the acid-volatile material is certainly not (CH(3))(2)Se and that it is probably H(2)Se. 4. The significance of these findings is discussed in relation to current knowledge about the metabolism and detoxication of selenium, and a scheme is proposed which incorporates this knowledge with recent observations on the interactions between trace amounts of selenium and tocopherol, and the production of acute selenium deficiency by Ag(+) in vitamin E-deficient rats.     

Ventilation and metabolic rate in the platypus: insights into the evolution of the mammalian breathing pattern

The platypus (Ornithorhyncus anatinus) is characterized by a rate of oxygen consumption (V(O2))that is higher than that reported for other similar sized monotremes, similar to marsupials and somewhat lower than eutherians. The platypus is also characterized by a breathing pattern, more typical of a diving mammal, with a high 'inspiratory drive' and a post-inspiratory pause. Further, the platypus reveals an attenuated hyperventilatory response to hypoxia and a reduced hyperpnoea to hypercapnia; such a response to these chemical stimuli is commonly observed in semi-fossorial and diving mammals. Nevertheless, under conditions of normoxia, ventilation (V(E))is matched to (V(O(2)) such that the convection requirement (V(E)/V(O2)) is similar to that reported for other mammals (approx. 37). The apparent consistency of the convection requirement in mammals suggests the blueprint for the design of the mammalian respiratory system has remained an interspecies constant in the three divergent extant sub-classes of mammals.     

Speculations on the evolution of the genetic code

An evolutionary scheme is postulated in which the bases enter the genetic code in a definite temporal sequence and the correlated amino acids are assigned definite functions in the evolving system.The scheme requires a singlet code (guanine coding for glycine) evolving into a doublet code (guanine-cytosine doublet coding for gly (GG), ala (GC), arg (CG), pro (CC)). The doublet code evolves into a triplet code. Polymerization of nucleotides is thought to have been by block polymerization rather than by a template mechanism. The proteins formed at first were simple structural peptides. No direct nucleotide-amino acid stereo-chemical interaction was required. Rather an adaptor-type indirect mechanism is thought to have been functioning since the origin.     

Characterization of the interactions between the nucleoprotein and the phosphoprotein of Henipavirus

The Henipavirus genome is encapsidated by the nucleoprotein (N) within a helical nucleocapsid that recruits the polymerase complex via the phosphoprotein (P). In a previous study, we reported that in henipaviruses, the N-terminal domain of the phosphoprotein and the C-terminal domain of the nucleoprotein (N(TAIL)) are both intrinsically disordered. Here we show that Henipavirus N(TAIL) domains are also disordered in the context of full-length nucleoproteins. We also report the cloning, purification, and characterization of the C-terminal X domains (P(XD)) of Henipavirus phosphoproteins. Using isothermal titration calorimetry, we show that N(TAIL) and P(XD) form a 1:1 stoichiometric complex that is stable under NaCl concentrations as high as 1 M and has a K(D) in the μM range. Using far-UV circular dichroism and nuclear magnetic resonance, we show that P(XD) triggers an increase in the α-helical content of N(TAIL). Using fluorescence spectroscopy, we show that P(XD) has no impact on the chemical environment of a Trp residue introduced at position 527 of the Henipavirus N(TAIL) domain, thus arguing for the lack of stable contacts between the C termini of N(TAIL) and P(XD). Finally, we present a tentative structural model of the N(TAIL)-P(XD) interaction in which a short, order-prone region of N(TAIL) (α-MoRE; amino acids 473-493) adopts an α-helical conformation and is embedded between helices α2 and α3 of P(XD), leading to a relatively small interface dominated by hydrophobic contacts. The present results provide the first detailed experimental characterization of the N-P interaction in henipaviruses and designate the N(TAIL)-P(XD) interaction as a valuable target for rational antiviral approaches.     

Analytic computation of the expectation of the linkage disequilibrium coefficient r2

The squared correlation coefficient r(2) (sometimes denoted Delta(2)) is a measure of linkage disequilibrium that is widely used, but computing its expectation E[r(2)] in the population has remained an intriguing open problem. The expectation E[r(2)] is often approximated by the standard linkage deviation sigma(d)(2), which is a ratio of two expectations amenable to analytic computation. In this paper, a method of computing the population-wide E[r(2)] is introduced for a model with recurrent mutation, genetic drift and recombination. The approach is algebraic and is based on the diffusion process approximation. In the limit as the population-scaled recombination rate rho approaches infinity, it is shown rigorously that the asymptotic behavior of E[r(2)] is given by 1/rho+O(rho(-2)), which, incidentally, is the same as that of sigma(d)(2). A computer software that computes E[r(2)] numerically is available upon request.     

The role of the lymphoid system in the regulation of the blood glucose level.

Recent findings have led to a new hypothesis in which it is proposed that the immune system plays a role in regulating the increase in blood glucose levels after a meal. The relevant findings are: (1) the primary lymphoid tissue, the lymph nodes are mostly present within adipose tissue depots throughout the body (there are at least 12 such depots and about 10 (12) lymphocytes, 99% of which are present in lymph nodes); (2) lymphocytes and other immune cells utilize glucose at a high rate but almost all of it is converted to lactate which accumulates in the cells prior to release; (3) glutamine, some of which is synthesized in muscle from glucose, is utilized at a high rate by immune cells, the end-product of which is mainly aspartate, which also accumulates in the cells prior to release; and (4) finally, there is a common blood supply to the lymph node and the adipose tissue depot and the blood flow through the depot and hence the node is increased after a meal. It is proposed that, after a meal, some of the absorbed glucose is taken up from the blood by the lymphocytes and converted to lactate and glutamine is converted to aspartate. These are released slowly into the blood from where they are removed and converted to glycogen by the liver. Hence the immune cells provide a temporary buffer for glucose in the form of lactate and aspartate and, in this way, restrict the rise in blood glucose during and after a meal.     

Systematisation of the arteries in the splenic hilus

156 abdominal preparations were explored by arteriography, corrosion and dissection. Within the meanders of the splenic artery a basic pattern can be traced. The division of the artery can easily be summarized by introducing the term of a truncus lienogastroepiploicus. The short gastric arteries are always present, and usually they are longer and more important than may appear from their name. In nearly half of the preparations (52%) an artery for the extremitas lienalis posterior is found; an artery for the extremitas lienalis anterior is very exceptional. A posterior gastric artery can be identified (36%) but it must be distinguished from several other vessels. The arteria colli pancreatis (for the neck of the pancreas) is a constant vessel that may have a superior (usually arteria lienalis) or an inferior origin (arteria mesenterica superior). It commonly supplies the transverse pancreatic artery and often the prepancreatic arcade. The arteria corporis pancreatis, too, is a constant artery. The pancreatic tail is thoroughly irrigated by usually more than one arteria caudae pancreatis. An important part of the greater curvature is not accompanied by the left gastroepiploic artery, but is supplied by the arteriae gastricae breves.     

The conservation of the biomass density and the age structure of the populations

A study was made of populations in stationary equilibrium that satisfy the following conditions: (1) The birth rate is very large in relation to the capacity of the habitat. (2) The part of the mortality which is independent of age is easily measured and is found to be very high. For these populations the following conclusions were drawn from the experimental observations: (1) The populations in steady state show an inversely proportional relation between the maximum average age of its components and the mortality. (2) The biomass of a population in a steady state saturating a habitat remains constant in spite of changes in the mortality. (3) The population of organisms continually growing through life, whose steady-state equilibria are reached under conditions of high mortality are composed of great numbers of individuals with a small average size. The equilibria which are reached under conditions of low mortality are characterized by a small number of individuals with large average size.     

Phosphotyrosine recognition domains: the typical, the atypical and the versatile

Infertility affects one in seven couples globally and has recently been classified as a disease by the World Health Organisation (WHO). While in-vitro fertilisation (IVF) offers effective treatment for many infertile couples, cases exhibiting severe male infertility (19?C57%) often remain difficult, if not impossible to treat. In such cases, intracytoplasmic sperm injection (ICSI), a technique in which a single sperm is microinjected into the oocyte, is implemented. However, 1?C5% of ICSI cycles still fail to fertilise, affecting over 1000 couples per year in the UK alone. Pregnancy and delivery rates for IVF and ICSI rarely exceed 30% and 23% respectively. It is therefore imperative that Assisted Reproductive Technology (ART) protocols are constantly modified by associated research programmes, in order to provide patients with the best chances of conception. Prior to fertilisation, mature oocytes are arrested in the metaphase stage of the second meiotic division (MII), which must be alleviated to allow the cell cycle, and subsequent embryogenesis, to proceed. Alleviation occurs through a series of concurrent events, collectively termed ??oocyte activation??. In mammals, oocytes are activated by a series of intracellular calcium (Ca²⁺) oscillations following gamete fusion. Recent evidence implicates a sperm-specific phospholipase C, PLCzeta (PLC??), introduced into the oocyte following membrane fusion as the factor responsible. This review summarises our current understanding of oocyte activation failure in human males, and describes recent advances in our knowledge linking certain cases of male infertility with defects in PLC?? expression and activity. Systematic literature searches were performed using PubMed and the ISI-Web of Knowledge. Databases compiled by the United Nations and World Health Organisation databases (UNWHO), and the Human Fertilization and Embryology Authority (HFEA) were also scrutinised. It is clear that PLC?? plays a fundamental role in the activation of mammalian oocytes, and that genetic, molecular, or biochemical perturbation of this key enzyme is strongly linked to human infertility where oocyte activation is deficient. Consequently, there is significant scope for our understanding of PLC?? to be translated to the ART clinic, both as a novel therapeutic agent with which to rescue oocyte activation deficiency (OAD), or as a prognostic/diagnostic biomarker of oocyte activation ability in target sperm samples.     

Dentin glycoprotein: the protein in the middle of the dentin sialophosphoprotein chimera

Dentin sialophosphoprotein (DSPP) is a major secretory product of odontoblasts and is critical for proper dentin formation. DSPP is believed to be processed into only two structural/functional domains: dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). Here we report the isolation and characterization of a third domain of DSPP, designated dentin glycoprotein (DGP). DGP was isolated from a guanidine/EDTA extract of porcine tooth dentin by ion exchange, hydroxyapatite affinity, size exclusion, and RP-HPL chromatography. Endoproteinase lysine C digestion products of DGP were characterized by Edman sequencing and mass spectrometry. The porcine DGP backbone is the 81-amino acid segment of DSPP (Ser392 to Gly472) between the DSP and DPP domains. DGP has four phosphorylated serine residues (Ser453, Ser455, Ser457, and Ser462) and one glycosylated asparagine (Asn397). There are no other post-translational modifications. DGP is a stains-all positive protein with an apparent molecular mass on SDS-PAGE of 19 kDa, which is reduced by glycopeptidase A digestion to 16 kDa. A variety of glycans can be linked to Asn397. All are complex biantennary structures with a common N-linked pentasaccharide core (mannose3-N-acetylglucosamine2), most with a fucosyl residue on the innermost N-acetylglucosamine. The alpha1-3 and alpha1-6 arms are always galactose beta1-4 N-acetylglucosamine beta1-2 mannose, and either or both arms can be unsialidated or monosialidated. The calculated monoisotopic molecular masses of the different glycosylated forms of the DGP phosphoprotein are: unsialidated 10,523 and 10,670, monosialidated 10,815 and 10,961, and disialidated 11,106, and 11,252 Da, with the disialidated forms being the most abundant.     

On the relationship between the non-photochemical quenching of the chlorophyll fluorescence and the Photosystem II light harvesting efficiency. A repetitive flash fluorescence induction study

Plants respond to excess light by a photoprotective reduction of the light harvesting efficiency. The notion that the non-photochemical quenching of chlorophyll fluorescence can be reliably used as an indicator of the photoprotection is put to a test here. The technique of the repetitive flash fluorescence induction is employed to measure in parallel the non-photochemical quenching of the maximum fluorescence and the functional cross-section (sigma(PS II)) which is a product of the photosystem II optical cross-section a(PS II) and of its photochemical yield Phi(PS II) (sigma (PS II) = a(PS II) Phi(PS II)). The quenching is measured for both, the maximum fluorescence found in a single-turnover flash (F(M) (ST)) and in a multiple turnover light pulse (F(M) (MT)). The experiment with the diatom Phaeodactylum tricornutum confirmed that, in line with the prevalent model, the PS II functional cross-section sigma (PS II) is reduced in high light and restored in the dark with kinetics and amplitude that are closely matching the changes of the F(M) (ST) and F(M) (MT) quenching. In contrast, a poor correlation between the light-induced changes in the PS II functional cross-section sigma (PS II) and the quenching of the multiple-turnover F(M) (MT) fluorescence was found in the green alga Scenedesmus quadricauda. The non-photochemical quenching in Scenedesmus quadricauda was further investigated using series of single-turnover flashes given with different frequencies. Several mechanisms that modulate the fluorescence emission in parallel to the Q(A) redox state and to the membrane energization were resolved and classified in relation to the light harvesting capacity of Photosystem II.     

Light reduces the excitation efficiency in the nss mutant of the sheep blowfly Lucilia

The nss (no steady state) phototransduction mutant of the sheep blowfly Lucilia was studied electrophysiologically using intracellular recordings. The effects of the nss mutation on the receptor potential are manifested in the following features of the light response. (a) The responses to a flash or to dim lights are close to normal, but the receptor potential decays close to the baseline level during prolonged illumination after a critical level of light intensity is reached. (b) The decline of the response is accompanied by a large reduction in responsiveness to light that recovers within 20 s in the dark. (c) The full reduction in responsiveness to light is reached when approximately 13% of the photopigment molecules are converted from rhodopsin (R) to metarhodopsin (M). (d) A maximal net pigment conversion from R to M by blue light induces persistent inactivation in the dark, without an apparent voltage response. This inactivation could be abolished at any time by M-to-R conversion with orange light. The above features of the mutant indicate that the effect of the nss mutation on the light response of Lucilia is very similar to the effects of the transient receptor potential (trp) mutation on the photoreceptor potential of Drosophila. Noise analysis and voltage measurements indicate that the decay of the receptor potential is due to a severe reduction in the rate of occurrence of the elementary voltage responses (bumps). The bumps are only slightly modified in shape and amplitude during the decline of the response to light of medium intensity. There is also a large increase in response latency during intense background illumination. These results are consistent with the hypothesis that separate, independent mechanisms determine bump triggering and bump shape and amplitude. The nss mutation affects the triggering mechanism of the bump.     

Controlling the ratchet effect through the symmetries of the systems: application to molecular motors

We discuss a novel generic mechanism for controlling the ratchet effect through the breaking of relevant symmetries. We review previous works on ratchets where directed transport is induced by the breaking of standard temporal symmetries f(t)=-f(t+T/2) and f(t)=f(-t) (or f(t)=-f(-t)). We find that in seemingly unrelated systems the average velocity (or the current) of particles (or solitons) exhibits common features. We show that, as a consequence of Curie's symmetry principle, the average velocity (or the current) is related to the breaking of the symmetries of the system. This relationship allows us to control the transport in a systematic way. The qualitative agreement between the present analytical predictions and previous experimental, numerical, and theoretical results leads us to suggest that for the given breaking of the temporal symmetries there is an optimal wave form for a given time-periodic force. Also, we comment on how this mechanism can be applied to the case where a ratchet effect is induced by breaking of spatial symmetries. Finally, we conjecture that the ratchet potential underlying biological motor proteins might be optimized according to the breaking of the relevant symmetries.     

Defining the proton entry point in the bacterial respiratory nitric-oxide reductase

The bacterial respiratory nitric-oxide reductase (NOR) is a member of the superfamily of O(2)-reducing, proton-pumping, heme-copper oxidases. Even although nitric oxide reduction is a highly exergonic reaction, NOR is not a proton pump and rather than taking up protons from the cytoplasmic (membrane potential-negative) side of the membrane, like the heme-copper oxidases, NOR derives its substrate protons from the periplasmic (membrane potential-positive) side of the membrane. The molecular details of this non-electrogenic proton transfer are not yet resolved, so in this study we have explored a role in a proposed proton pathway for a conserved surface glutamate (Glu-122) in the catalytic subunit (NorB). The effect of substituting Glu-122 with Ala, Gln, or Asp on a single turnover of the reduced NOR variants with O(2), an alternative and experimentally tractable substrate for NOR, was determined. Electron transfer coupled to proton uptake to the bound O(2) is severely and specifically inhibited in both the E122A and E122Q variants, establishing the importance of a protonatable side chain at this position. In the E122D mutant, proton uptake is retained but it is associated with a significant increase in the observed pK(a) of the group donating protons to the active site. This suggests that Glu-122 is important in defining this proton donor. A second nearby glutamate (Glu-125) is also required for the electron transfer coupled to proton uptake, further emphasizing the importance of this region of NorB in proton transfer. Because Glu-122 is predicted to lie near the periplasmic surface of NOR, the results provide strong experimental evidence that this residue contributes to defining the aperture of a non-electrogenic "E-pathway" that serves to deliver protons from the periplasm to the buried active site in NOR.     

On the Gompertzian growth in the fractal space-time

An analytical approach to determination of time-dependent temporal fractal dimension b(t)(t) and scaling factor a(t)(t) for the Gompertzian growth in the fractal space-time is presented. The derived formulae take into account the proper boundary conditions and permit a calculation of the mean values b(t)(t) and a(t)(t) at any period of time. The formulae derived have been tested on experimental data obtained by Schrek for the Brown-Pearce rabbit's tumor growth. The results obtained confirm a possibility of successful mapping of the experimental Gompertz curve onto the fractal power-law scaling function y(t)=a(t)tb(t) and support a thesis that Gompertzian growth is a self-similar and allometric process of a holistic nature.     

Influence of the pK(a) value of the buried, active-site cysteine on the redox properties of thioredoxin-like oxidoreductases

Thioredoxin constitutes the prototype of the thiol-disulfide oxidoreductase family. These enzymes contain an active-site disulfide bridge with the consensus sequence Cys-Xaa-Xaa-Cys. The more N-terminal active-site cysteine is generally a strong nucleophile with an abnormal low pK(a) value. In contrast, the more C-terminal cysteine is buried and only little is known about its effective pK(a) during catalysis of disulfide exchange reactions. Here we have analyzed the pK(a) values of the active-site thiols in wild type thioredoxin and a 400-fold more oxidizing thioredoxin variant by NMR spectroscopy, using selectively (13)C(beta)-Cys-labeled proteins. We find that the effective pK(a) of the buried cysteine (pK(b)) of the variant is increased, while the pK(a) of the more N-terminal cysteine (pK(N)) is decreased relative to the corresponding pK(a) values in the wild type. We propose two empirical models which exclusively require the knowledge of pK(N) to predict the redox properties of thiol-disulfide oxidoreductases with reasonable accuracy.     

Speculations on the evolution of the genetic code.

An evolutionary scheme is postulated in which the bases enter the genetic code in a definite temporal sequence and the correlated amino acids are assigned definite functions in the evolving system. The scheme requires a singlet code (guanine coding for glycine) evolving into a doublet code (guanine-cytosine doublet coding for gly (GG), ala (GC), arg (CG), pro (CC). The doublet code evolves into a triplet code. Polymerization of nucleotides is thought to have been by block polymerization rather than by a template mechanism. The proteins formed at first were simple structural peptides. No direct nucleotide-amino acid stereo-chemical interaction was required. Rather an adaptor-type indirect mechanism is thought to have been functioning since the origin.     

Balancing the central roles of the thylakoid proton gradient

The photosynthetic electron transfer chain generates proton motive force (pmf), composed of both electric field (Deltapsi) and concentration (DeltapH) gradients. Both components can drive ATP synthesis, whereas the DeltapH component alone can trigger feedback regulation of the antenna. It has often been suggested that a relatively large pmf is needed to sustain the energetic contributions of the ATP synthase reaction (DeltaG(ATP)), and that the Deltapsi component is dissipated during illumination, leading to an acidic lumen in the light. We suggest that this is incompatible with the stabilities of lumenal components and the observed activation of downregulation. Recent work on the chloroplast ATP synthase suggests that a more moderate pmf can sustain DeltaG(ATP). In addition, in vivo probes suggest that a substantial fraction of pmf can be stored as Deltapsi. Together, these factors should allow sufficient DeltaG(ATP) to maintain lumen pH in a range where lumenal enzyme activities are nearly optimal, and where the level of NPQ is regulated.     

Properties of the apo-form of the NADP(H)-binding domain III of proton-pumping Escherichia coli transhydrogenase: implications for the reaction mechanism of the intact enzyme

Proton-translocating nicotinamide nucleotide transhydrogenases contain an NAD(H)-binding domain (dI), an NADP(H)-binding domain (dIII) and a membrane domain (dII) with the proton channel. Separately expressed and isolated dIII contains tightly bound NADP(H), predominantly in the oxidized form, possibly representing a so-called "occluded" intermediary state of the reaction cycle of the intact enzyme. Despite a K(d) in the micromolar to nanomolar range, this NADP(H) exchanges significantly with the bulk medium. Dissociated NADP(+) is thus accessible to added enzymes, such as NADP-isocitrate dehydrogenase, and can be reduced to NADPH. In the present investigation, dissociated NADP(H) was digested with alkaline phosphatase, removing the 2'-phosphate and generating NAD(H). Surprisingly, in the presence of dI, the resulting NADP(H)-free dIII catalyzed a rapid reduction of 3-acetylpyridine-NAD(+) by NADH, indicating that 3-acetylpyridine-NAD(+) and/or NADH interacts unspecifically with the NADP(H)-binding site. The corresponding reaction in the intact enzyme is not associated with proton pumping. It is concluded that there is a 2'-phosphate-binding region in dIII that controls tight binding of NADP(H) to dIII, which is not a required for fast hydride transfer. It is likely that this region is the Lys424-Arg425-Ser426 sequence and loops D and E. Further, in the intact enzyme, it is proposed that the same region/loops may be involved in the regulation of NADP(H) binding by an electrochemical proton gradent.