Crystallography of hemerythrin

X-ray crystallographic studies of hemerythrin from Golfingia gouldii show that the molecules pack in a tetragonal cell with two sets of molecules in an apparently face-centred array seen in projection along the 4-fold axis, but displaced relatively to each other by approximately $\text{c}\text{10}$ in the axial direction. Both sets of molecules lie on 4-fold rotation axes, so that the subunits of each octameric molecule are related in pairs by a molecular 4-fold rotation axis. The two subunits of each pair are probably related by non-crystallographic 2-fold rotation axes perpendicular to the 4-fold axes and lying at 10 ° and 55 ° to the a and b axes. At low resolution the subunits are apparently arranged approximately in the form of a square prism. Along each 4-fold crystallographic axis there are two hemerythrin molecules, nearly equidistant and having similar but not identical orientations.     

On the mechanism of interaction between histone I and DNA and histone III and DNA

A mechanism is suggested at the molecular level whereby histone I can act as a cross-link, or strut, between two DNA strands involved in packing the DNA molecule into the confined space of the chromosome. The amino acid sequence of the N-terminal region is known (to 72). It is suggested that this portion is composed of three main functionally distinct segments: (1) (amino acids 1–18) that forms a broken a-helix (by pro) packed into the depths of the major groove; (2) (amino acids 19–35), rich in lys, which forms a “roof” over segment (1) with nine ionic bonds to phosphate; and (3) (amino acids 41–69) which forms an a-helix. Thus segments (1) and (2) grip the DNA helix and segment (3) forms a strut between two DNA strands. Presumably the rest of the histone molecule forms a second lys-rich “hand” grasping the second DNA helix.The amino acid sequence of histone III suggests that it provides a variant on this thesis. In this case the ionic links to phosphate and the packing of the major groove are provided by successive segments of the protein (e.g. a sequence -arg-lys- followed by a β-turn or a short segment of a-helix). This covers amino acids 1–87. The next segment (88–114) forms an a-helix and the last segment (115–135) repeats the structure of the first segment. Thus histone III might also form cross-links between two parallel DNA strands but its attachment is markedly asymmetrical with one “hand” composed of 87 amino acids filling over $\text{1}\text{1}\text{2}$ turns of the major groove and the other “hand” composed of only 20 amino acids.     

Antenna function of a chlorophyll ab protein complex of Photosystem I

The functional role of a chlorophyll $\text{a}\text{b}$ complex associated with Photosystem I (PS I) has been studied. The rate constant for P-700 photooxidation, K_P-700, which under light-limiting conditions is directly proportional to the size of the functional light-harvesting antenna, has been measured in two PS I preparations, one of which contains the chlorophyll $\text{a}\text{b}$ complex and the other lacking the complex. K_P-700 for the former preparation is half of that of the preparation which has the chlorophyll $\text{a}\text{b}$ complex present. This difference reflects a decrease in the functional light-harvesting antenna in the PS I complex devoid of the chlorophyll $\text{a}\text{b}$ complex. Experiments involving reconstitution of the chlorophyll $\text{a}\text{b}$ complex with the antenna-depleted PS I preparation indicate a substantial recovery of the K_P-700 rate. These results demonstrate that the chlorophyll $\text{a}\text{b}$ complex functions as a light-harvesting antenna in PS I.     

The further investigation of physical and photochemical properties of quasimetacyclophane derived from thymine

The thymine derived quasimetacyclophane exist in two conformers $\text{a}$ and $\text{b}$. The absorption spectra of $\text{a}$ and $\text{b}$ were evaluated and the conformational equilibrium in different solvents /H₂O : EtOH/ were examined. The rate constant k_?1 for reaction $\text{b}\text{→}\text{a}$ was established as well as E_a.     

Resolution of the light-harvesting chlorophyll ab-protein of Vicia faba chloroplasts into two different chlorophyll-protein complexes

Thylakoids of Vicia faba chloroplasts disaggregated by sodium dodecyl sulfate were separated by means of different electrophoretic systems. Under the conditions of a high resolving gel system the chlorophyll containing zone previously termed chlorophyll-protein complex II or light-harvesting chlorophyll $\text{a}\text{b}\text{-}\text{protein}$ was found to be inhomogeneous. It represents a mixture of two distinct chlorophyll-proteins characterized by different spectral properties and different apoproteins. One chlorophyll-protein exhibits a chlorophyll $\text{a}\text{b}$ ratio of 0.9 and is associated with polypeptides of 24 000 and 23 000 daltons. The 24 000 dalton band is proved to bind chlorophyll and has a light-harvesting function. The function of the 23 000 dalton band is unknown. The second chlorophyll-protein has a chlorophyll $\text{a}\text{b}$ ratio of 2.1 and an additional absorption maximum in the position of 637 nm. It is associated with only one polypeptide which has an apparent molecular weight of 23 000. The two 23 000 dalton polypeptides occurring in both complexes are not identical.     

Cycloheximide inhibition of insulin control of liver glycogen synthase b into a conversion.

Cycloheximide given to insulin-treated alloxan diabetic rats results in the inhibition of insulin-induced liver glycogen synthase $\text{b}\text{into}\text{a}$ conversion without affecting the level of synthase $\text{b}$. The effect of cycloheximide, believed to elevate cAMP in liver of normal rats, is independent of cAMP levels of the insulin-treated diabetic rat. The inhibition of insulin-mediated synthase $\text{b}$ to $\text{a}$ conversion by cycloheximide does not appear to be the result of a cycloheximide-induced cAMP-dependent phosphorylation of synthase $\text{a}$ to $\text{b}$ and suggests that insulin control of synthase $\text{b}$ and $\text{a}$ interconversions is dependent upon cycloheximide-sensitive protein synthesis.     

Electron microscopy of muscle phosphorylase a

Electron microscopy of negatively stained preparations of phosphorylase a (tetrameric form) from solutions with and without added protamine revealed three characteristic types of particle images. In preparations with added protamine several types of crystalline formation were observed: three types of plane monolayers, tubes and small three-dimensional crystals. The tubes have been studied by optical diffraction and filtering. In the main class of tubes the particles form $\text{26}\text{9}$ three-start helices (it may well be that narrow tubes with different parameters exist). Now and again, one can observe tubes twice as large in diameter, and tubes with two-layer walls. Analysis of the images of particles in solution and in crystalline formations showed that their structure can be characterized in terms of one model consisting of four elongated bent subunits arranged with the point-group symmetry 222 at the vertices of a tetrahedron. The structure of phosphorylase b particles, previously studied (Kiselev et al., 1971), can also be characterized satisfactorily by the same model. The difference in the structure of these two forms expresses itself in a different character of mutual aggregation of the molecules in plane layers, and in the parameters of the helical packing of the molecules in tubes.     

Specificity of human histocompatibility antigen reactive cells in vitro. Separate cell populations responsive to the products of each major histocompatibility system (MHS) haplotype

One-way mixed lymphocyte cultures were established between related cell donors A (haplotype designated $\text{a}\text{b}$) and B ($\text{a}\text{c}$). The cells from A, proliferating in response to stimulation by mitomycin treated cells from B, were eliminated from the culture by a hot pulse of ³H-thymidine. A marginal response was observed when the remaining cells from A reencountered additional stimulating cells from B, or cells from an HL-A identical sibling to B. In addition, the remaining responding cells were virtually incapable of responding to secondary stimulation by family member C ($\text{b}\text{c}$), who shared one haplotype (b) with individual A and the other haplotype (c) with the individual stimulating cell donor B. The MLC secondary stimulation response to family member D ($\text{c}\text{d}$), who differed from A by both haplotypes, but shared one haplotype with B, was reduced to approximately 50% of control values. In other experiments it was found possible to completely eliminate the response of A ($\text{a}\text{b}$) to D ($\text{c}\text{d}$) by using a combination of stimulating cells from related donors B ($\text{a}\text{b}$) and C ($\text{b}\text{c}$) in the initial hot pulse MLC.Separate populations of responding cells reactive to antigenic products of each major histocompatibility system haplotype is a likely explanation of these observations.     

Quantitative separation of spinach thylakoids into Photosystem II-enriched inside-out vesicles and Photosystem I-enriched right-side-out vesicles

Yeda press disruption of thylakoids in the presence of magnesium followed by aqueous polymer two-phase partitioning fractionated the total thylakoid membrane material into two distinctly different fractions. One fraction comprised approx. 60% of the material on a chlorophyll basis and contained inside-out vesicles while the other fraction (40%) contained right-side-out vesicles. The sidedness of the vesicles was determined from the direction of their light-induced proton translocation. The inside-out vesicles showed a pronounced Photosystem (PS) II enrichment as judged by their high PS II and low PS I activities. Moreover, they showed a high ratio between the PS II reaction centre chlorophyll-protein complex and the PS I reaction centre chlorophyll-protein complex (CP I). The chlorophyll $\text{a}\text{b}$ ratio was as low as 2.3 compared to 3.2 for the starting material. In contrast, the right-side-out vesicles showed a pronounced PS I enrichment. Their chlorophyll $\text{a}\text{b}$ ratio was 4.3–4.9. The tight stacking induced by Mg²⁺ allows a quantitative formation of inside-out vesicles from the appressed thylakoid regions while mainly non-appressed thylakoids turn right-side-out. The possibility of fractionating all of the thylakoid material into two sub-populations with markedly different composition with respect to PS I and PS II argues against a close physical association between the two photosystems and in favour of their spatial separation in the plane of the membrane. This fractionation procedure, which can be completed within 1 h and gives high yields of both PS II inside-out thylakoids and PS I right-side-out thylakoids, should be very useful for facilitating and improving studies on both the transverse and lateral organization of the thylakoid membrane.     

The nature of the light-harvesting complex as defined by sodium dodecyl sulfate polyacrylamide gel electrophoresis

Reelectrophoresis of the oligomer form (CP II1) of the chlorophyll $\text{a}\text{b}$ light-harvesting complex (LHC) from the green alga Acetabularia yields two green bands which run at the position typical of the monomer (CP II). The upper green band (CP II₁) is enriched in the 27 kDa polypeptide of the LHC, while the lower is enriched in the 26 kDa polypeptide. The fact that both bands have both chlorophyll (Chl) a and b, and in the same ratio, implies that the LHC is made up of two Chl $\text{a}\text{b}$ proteins. Neither of these bands can be attributed to the Chl $\text{a}\text{b}$ complex ‘CP 29’ (Camm, E.L. and Green, B.R. (1980) Plant Physiol. 66, 428–432). Resolution of CP II₁ and CP II₂ of spinach can be obtained if sucrose gradient fractions of an octylglucoside extract are subjected to SDS-polyacrylamide gel electrophoresis. CP II₁ and CP II₂ are interpreted as being fundamental subunits of the light-harvesting complex as it is defined on SDS-polyacrylamide gels.     

Regulation of muscle phosphorylase activity by carnosine and anserine

Carnosine (β-alanyl-L-histidine) activates rabbit muscle phosphorylase $\text{a}$ in the presence and absence of AMP and phosphorylase $\text{b}$ in the presence of AMP in a biphasic manner with a maximal activation at about 50mM carnosine and with phosphorylase $\text{b}$ showing a greater degree of activation than phosphorylase $\text{a}$. Anserine (β-alanyl-L-N^π-methyl-histidine) activates phosphorylase $\text{a}$ to a lesser extent than carnosine up to a concentration of 90mM, whereas with phosphorylase $\text{b}$ a weak activation below 30mM and a concentration-dependent inhibition above this concentration occurs. These effects are specific for the dipeptides and are not shown by their constituent amino acids. Carnosine and anserine activate phosphorylase $\text{a}$ in the presence of the allosteric inhibitors ATP, D-glucose and caffeine, and the inhibition of phosphorylase $\text{b}$ by anserine is also observed in the presence of these inhibitors.     

Enhancement of lymphocyte dependent antibody cytotoxicity by anti allotype serum.

Anti-allotype b4 and anti-allotype a3 antibody as well as heterologous anti-rabbit IgG enhanced the lymphocyte-dependent antibody cytotoxicity, in a system using chicken red blood cells (ChRBC) coated with rabbit anti-ChRBC antibody ($\text{a}\text{3}\text{a}\text{3}$, $\text{b}\text{4}\text{b}\text{5}$) as target cells and rabbit lymphocytes ($\text{a}\text{3}\text{a}\text{3}$, $\text{b}\text{4}\text{b}\text{5}$). No enhancement was observed with anti-allotype b6 antiserum, nor with heterologous anti-rabbit IgM, IgA, and Fc antibodies. Cytotoxicity mediated by spleen, bone marrow, and thymus lymphocytes was enhanced by anti-allotype antibody. The enhancement of cytotoxicity by anti-allotype antibody cannot be attributed to lymphocyte proliferation but is more likely related to the formation of an additional bridge between effector cell and target cell.     

In vitro activation of leukocyte glycogen synthetase

The activity of leukocyte glycogen synthetase in a freshly prepared homogenate is almost completely in the $\text{b}$ form. Incubation of the homogenate at 30°C caused a time dependent increase in the activity measured in the absence of G-6-P ($\text{b}$ to $\text{a}$ conversion). The K_a for G-6-P decreased from 0.7 to 0.01 mM. Freezing of the homogenate resulted in a complete loss of the capacity for activation. These results demonstrate that glycogen synthetase from leukocytes of normal human subjects can be converted $\text{in vitro}$ to a form, which is almost independent of G-6-P for activity.     

Fluorescence properties of chlorophyll a and b monomolecular films at the air-water interface

The fluorescence properties of chlorophyll $\text{a}$ and $\text{b}$ monomolecular films at the air-water interface were measured by a high sensitivity fluorophotometer using the photon-counting method. The fluorescence intensity of chlorophyll molecules in monomolecular films in the absence of any diluents did not decrease simply with the mean distance of chlorophyll molecules. Over the range of the mean distances from 27 to 21 Å, three fluorescence components (peaks at 685, 695 and 715 nm) of chlorophyll $\text{a}$ were observed. In the case of chlorophyll $\text{b}$, two fluorescence components (peaks at 667 and 685 nm) were observed over the range of the mean distances from 34 to 24 Å. When the mean distance was 18 Å, the short wavelength component of chlorophyll $\text{b}$ disappeared, and only the long wavelength component was observed.     

Low-intensity subnanosecond fluorescence study of the light-harvesting chlorophyll ab protein

The fluorescence decay characteristics of the isolated light-harvesting chlorophyll $\text{a}\text{b}$ protein have been studied using low-intensity subnanosecond-resolution time-correlated single-photon counting. In the monomeric state in detergent micelles, the chlorophyll $\text{a}\text{b}$ protein exhibits biexponential decay (τ₁ = 1.2 ns, τ₂ = 3.3 ns) with the two components having very similar weights. The decay parameters do not depend on emission wavelength. These results are discussed in relation to the Van Metter-Knox-Shepanski model (Van Metter, R.M. (1977) Biochim. Biophys. Acta 462, 642–657; Shepanski, J.S. and Knox, R.S. (1982) Isr. J. Chem., in the press) of the chlorophyll $\text{a}\text{b}$ protein, and a kinetic analysis of the energy-transfer processes. The influence of detergent composition and concentration on the fluorescence decay of the chlorophyll protein is also described.     

Electron diffraction study on single crystals of l-type and dl-type lecithins

An electron diffraction study was carried out on thin single micro-crystals of l-type and dl-type dipalmitoyl lecithins grown in xylene suspensions and fine net patterns were obtained and the mechanism of the thermotropic phase transitions of them was clarified.From the apparent structure of diffraction patterns in low temperature, it is confirmed that the two dimensional lattices have p mm symmetry in l-type and in dl-type lecithins. Lattice parameters from the [001] projection are $\text{d}{}_{100}\text{= 9.9}\text{A}\text{?}$ and $\text{d}{}_{010}\text{= 8.8}\text{A}\text{?}$ in l-type, and $\text{d}{}_{100}\text{= 17.2}\text{A}\text{?}$ and $\text{d}{}_{010}\text{= 8.9}\text{A}\text{?}$ in dl-type.With anisotropic variation of dimensions along a and b axes, i.e. contraction for a and expansion for b, induced by temperature rise by electron irradiation during the observation, these diffraction patterns of the lattices of l-type and dl-type were transformed into those characterized by the six diffraction spots having nearly the same spacings. Four of them are observed on slightly outer and two are slightly inner positions as compared with their mean spacings of about (4.1 Å)^?1 in l-type and about (4.2 Å)^?1 in dl-type. The changes in the patterns observed indicate that at low temperatures the hydrocarbon chains are nearly perpendicular to the layer in dl-type lipid, and tilted with a more complicated packing in l-type ones. The dimension along a in dl-type is twice as large as that in l-type.     

Substrate specificity of glycogen synthase phosphatase from bovine heart: action on phosphorylase a and histone

Glycogen synthase phosphatase has been purified from bovine heart. This preparation catalyzes conversion of synthase D into I and phosphorylase $\text{a}$ into $\text{b}$ and is able to dephosphorylate synthase D, phosphorylase $\text{a}$, active phosphorylase kinase, and phosphorylated histone and casein. The activity of phosphatase was assayed with synthase D, phosphorylase $\text{a}$, and histone as substrates after chromatography on Sephadex G-100, after sucrose gradient centrifugation, and after isoelectric focusing in a sucrose gradient. In all cases no separation of enzyme activity was observed with the above substrates. The phosphatase activity on all substrates was lost at the same rate by heat denaturation. These results indicate that this enzyme preparation contains a single phosphoprotein phosphatase which is responsible for the activity observed on the above substrates.     

Titles of related papers in other sections

Electrophoretic analysis by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis showed that the light-harvesting chlorophyll $\text{a}\text{b}\text{-}\text{protein}$ complex of barley thylakoids contains only one polypeptide of apparent molecular weight 26 000. The barley mutant, deficient in chlorophyll b and this light-harvesting complex, lacks this polypeptide.The addition of a nonionic detergent, Triton X-100, to the sodium dodecyl solubilization buffer prior to SDS polyacrylamide tube gel electrophoresis, allowed separation of a relatively stable complex, characterized as an oligomeric form of the light-harvesting complex. The oligomer also contained a polypeptide with an apparent molecular weight of 26 000. The absorption and fluorescence spectral properties of the oligomer are similar to those of the monomer. It is suggested that the oligomer of the light-harvesting chlorophyll $\text{a}\text{b}\text{-}\text{protein}$ is closer to the in vivo form rather than the monomer.     

Amino acid sequence of the heme a subunit of bovine heart cytochrome oxidase and sequence homology with hemoglobin.

The amino acid sequence of the 11.6 K dalton heme $\text{a}$ subunit of bovine heart cytochrome oxidase has been completed and is presented here. The sequence investigation has established the positions in the protein of all the possible heme ligands, namely cysteine, methionine, histidine and lysine residues. However, the isolation conditions may have caused the heme $\text{a}$ to migrate from its original site or the heme is caged by peptides as pointed out in Reference 6. The sequence of the heme $\text{a}$ subunit and the β-chain of hemoglobin shows homology. It is possible that these two proteins have arisen from a common ancestor in the distant past.     

Crystal structure of the low-dimensional uranium pentatelluride: UTe5

The crystal structure of UTe₅ (a = 17.915(5), b = 10.407(3), c = 4.220(2) Å, Pnma, Pn2₁a, Z =4) was refined from 822 intensities with I>3σ(I) to a conventional R factor of 0.060. The uranium coordination polyhedron is a three capped tellurium trigonal prism, and all the Te atoms are involved in TeTe bonds. The structure is built up with infinite chains of prisms stacked in the $\text{c}$ direction. The chains are linked into (b, c) layers by a single Te atom which exhibits some positional disorder.