Human psychophysics: Functional interpretation for contrast sensitivity versus spatial frequency curve

The hypothesis that neural processing in the human visual pathways compensates for both optical degradation as well as noise contamination at the photoreceptor level is introduced and shown to be consistent with the high frequency portion of the contrast sensitivity function for threshold detection of sinusoidal gratings in addition to the suprathreshold phenomenon of matching sinusoidal gratings of different spatial frequencies. This offers a unifying interpretation for why, at threshold conditions, the high spatial frequency portion of the image is blurred as severely by the nervous system as it is by the optics (e.g. Campbell and Green, 1965) while in extreme suprathreshold conditions the nervous system effectively deblurs the image (e.g. Georgeson and sullivan, 1975; Kulikowski, 1976). These conclusions do not necessitate a highly specific form of visual processing such as Fourier channeling.This research was conducted at Yale University, Department of Ophthalmology and Visual Science, New Haven, Connecticut, USA, throughout which period A.W.S. was a John Simon Guggenheim fellow     

Effect of Temperature on Blue-Green Algae (Cyanobacteria) in Lake Mendota

The temperature optimum for photosynthesis of natural populations of blue-green algae (cyanobacteria) from Lake Mendota was determined during the period of June to November 1976. In the spring, when temperatures ranged from 0 to 20°C, there were insignificant amounts of blue-green algae in the lake (less than 1% of the biomass). During the summer and fall, when the dominant phytoplankton was blue-green algae, the optimum temperature for photosynthesis was usually between 20 and 30°C, whereas the environmental temperatures during this period ranged from 24°C in August to 12°C in November. In general, the optimum temperature for photosynthesis was higher than the environmental temperature. More importantly, significant photosynthesis also occurred at low temperature in these samples, which suggests that the low temperature alone is not responsible for the absence of blue-green algae in Lake Mendota during the spring. Temperature optima for growth and photosynthesis of laboratory cultures of the three dominant blue-green algae in Lake Mendota were determined. The responses of the two parameters to changes in temperature were similar; thus, photosynthesis appears to be a valid index of growth. However, there was little photosynthesis by laboratory cultures at low temperatures, in contrast to the natural samples. Evidence for an interaction between temperature and low light intensities in their effect on photosynthesis of natural samples is presented.     

Congruency of phylogenies derived from different proteins

Summary This communication examines the question of phylogenetic congruency- i.e., whether or not the branching order of evolutionary trees is independent of the protein studied. It was found that trees constructed for birds on the basis of immunological comparison of their transferrins, albumins, and ovalbumins agree approximately with a published tree based on the amino acid sequences of their lysozymesc. This congruency is especially noteworthy with respect to the phylogenetic position of the chachalaca, a Mexican bird classified on morphological grounds in the family Cracidae of the order Galliformes. At the protein level, this species differs as much from non-cracid galliform birds as does the duck, which belongs to another order. Despite the organismal similarity between cracid and non-cracid galliform birds, the molecular relationship is remote. If this contrast between organismal and molecular results had been based on comparative studies with only lysozyme, one could have ascribed the contrast to the possibility that chachalaca lysozyme was paralogous, rather than orthologous, to the other bird lysozymesc. Examination of several proteins is thus desirable in cases of possible paralogy.This work was supported in part by grants GB-42028X from NSF and GM-21509 from NIH     

Amino acid sequence and immunological properties of chachalaca egg white lysozyme

Summary The amino acid sequence of lysozyme c from chachalaca egg white was determined. Like other bird lysozymes c, that of the chachalaca has 129 amino acid residues. It differs from other avian lysozymes c by 27 to 31 amino acid substitutions as well as by being devoid of phenylalanine. It contains substitutions at 9 positions which are invariant in the other 7 bird lysozymes of known sequence. Although the chachalaca is classified zoologically in the order Galliformes, which includes chickens and other pheasant-like birds, its lysozyme differs more from those of pheasant-like birds than do the lysozymes c of ducks. Phylogenetic analysis of the sequence comparisons confirms that the lineage leading to chachalaca lysozyme c separated from that leading to other galliform lysozymes c before the duck lysozyme c lineage did. This indicates a contrast between protein evolution and evolution at the organismal level. Immunological comparison of chachalacalysozyme c with other lysozymes of known sequence provides further support for the proposal that immunological cross-reactivity is strongly dependent on degree of sequence resemblance among bird lysozymes.103rd communication on lysozymes from the Laboratory of P. Jollès. Supported in part by grants from C.N.R.S. (ER 102), I.N.S.E.R.M. (Groupe de recherche U-116), N.S.F. (GB-42028X), and N.I.H. (GM-21509).     

The tyrosinase activity of melanosomes from the harding-passey melanoma: The absence of a peroxidase component in vitro

Melanosomes were isolated from the Harding-Passey melanoma with a density gradient technique. Using the Pomerantz radioassay for tyrosinase activity it was found that these isolated melanosomes could hydroxylate tyrosine in the presence of catalase sufficient to deny the enzyme any hydrogen peroxide. It was further found that the rate of hydroxylation was unaffected by the presence of exogenous hydrogen peroxide. Tyrosinase activity could be suppressed by preincubation in diethyldithiocarbamate followed by removal of this inhibitor before enzyme assay. Attempts to regain enzymatic activity, however, by addition of copper II ions were unsuccessful. No peroxidase activity could be detected on the isolated granules, and indeed evidence for a peroxidase inhibitor on the granules was found. It was also found that the peroxidase activity present in a 20% homogenate of mouse muscle did not demonstrate any tyrosinase activity with the Pomerantz assay even in the presence of hydrogen peroxide. It is concluded from these studies that there is tyrosinase on these melanosomes which is capable in vitro of hydroxylating tyrosine without any contribution from an active peroxidase.     

Enhanced synthesis de novo of phosphatidylinositol in lymphocytes treated with cationic amphiphilic drugs.

A variety of amphiphilic cations caused very large increases in the rates of incorporation of Pi and glycerol into phosphatidylinositol in pig mesenteric small lymphocytes. This synthesis de novo of phosphatidylinositol led to a doubling of the phosphatidylinositol concentration in the cells within 3.5 h. The increase in synthesis of phosphatidylinositol labelled with [3H]- or [14C]-glycerol was matched by an approximately equivalent decrease in incorporation of glycerol into phosphatidylcholine, phosphatidylethanolamine and triacylglycerol. Amphilic cations which produced these effects included, in order of decreasing effectiveness, trifluoperazine (half-maximal effect at about 70 mum) greater than chlorpromazine approximately promethazine approximately imipramine greater than cinchocaine greater than amethocaine approximately cetyltrimethylammonium greater than fenfluramine greater than amphetamine greater than 2-phenethylamine greater than cocaine approximately procaine; the most effective compounds were those with the largest and most hydrophobic non-polar substituents. The response to cations was not changed by varying the extracellular Ca2+ concentration in the range 10 nm-1mm. The active amphiphilic cations interacted with anionic phospholipids causing aggregation of aqueous dispersions and/or changes in chromatographic behaviour. These results indicate that amphiphilic cations redirect glycerolipid synthesis de novo, probably owing to inhibition of phosphatidate phosphohydrolase, so that phosphatidylinositol synthesis is increased at the expense of other glycerolipids.     

Immune Complexes in Cystic Fibrosis

Circulating immune complexes were detected in serum and sputum of patients with cystic fibrosis (C.F.). There were extensive deposits of immunoglobulins and complement immune complexes in several of the C.F. organs, especially the respiratory and gastrointestinal tracts, but not in the kidneys. Significant concentrations of IgG and of complement complexes could be eluted from the lungs of the C.F. patients but not from those of controls. Studies involving immunoabsorption, autoradiography, and molecular sieving through Sephadex G-200 columns identified both bovine serum albumin and staphylococcal α-haemolysin as two of the antigens present in the immune complexes. The sedimentation constant of the immune complexes was about 8S to 11S. The clinical significance of these immune complexes and the wide variety of antibodies detected in C.F. patients are discussed.     

Recognition at cell surfaces: phytohaemagglutinin-lymphocyte interaction.

Many aspects of cell behaviour are regulated by the interaction of extracellular ligands with specific receptors exposed on the cell surface. The receptors correspond to membrane proteins and expecially glycoproteins. A key event in regulation is the transmission across the surface membrane of the information resulting from receptor-ligand interaction. The activation of lymphocytes by Phaseolus vulgaris phytohaemagglutinin (PHA) provides a convenient experimental model for the study of the molecular basis of receptor-ligand interaction and the molecular consequences of interaction. The receptor mediating lymphocyte activation by PHA is probably a unique glycoprotein which is present to the extent of about 3 X 10(4) molecules/cell. The PHA-receptor complex solubilized in 1% sodium deoxycholate has a molecular size of about 3 X 10(5). The primary event in the activation process is probably an increase in the permeability of the surface membrane to Ca2+. This may be achieved by PHA cross-linking ('patching') the receptors to form a polar channel that permits an influx of Ca2+.     

The presence and binding characteristics of calmodulin in microsomal preparations enriched in sarcoplasmic reticulum from rabbit skeletal muscle

ATP-dependent oxalate facilitated calcium transport in sarcoplasmic reticulum (SR) preparations obtained from rabbit vastus lateralis muscle (fast skeletal muscle; F_sr) and soleus (slow skeletal muscle; S_sr) was determined. Addition of exogenous calmodulin did not stimulate calcium transport in either F_sr or S_sr preparations. F_sr and S_sr previously washed in 1 mM EGTA demonstrated a reduced capacity to transport Ca²⁺; the exogenous addition of calmodulin (0.24 μM) under these conditions, did not restore uptake activity but significantly decreased the steady-state level of Ca²⁺ uptake. Extracts of skeletal SR prepared by treatment with 0.2 mM EDTA and boiling produced significantly more stimulation of red cell Ca²⁺ATPase activity than extracts prepared by boiling alone. This stimulation of red cell Ca²⁺-ATPase was inhibited to a significant extent by $\text{48}\text{80}$, a known anti-calmodulin agent. Radioimmunoassay revealed that extracts prepared by boiling or EDTA-treatment followed by boiling contained considerable amounts of calmodulin. Washing with 1 mM EGTA, though, did not release any calmodulin from SR. These studies reveal that calmodulin is present in both F_sr and S_sr and can only be removed by harsh treatments. The role of calmodulin in skeletal muscle Ca²⁺-transport remains to be determined.     

Inhibitors of lipoxygenase products improve survival in traumatic shock

We have used three selective inhibitors of arachidonic acid metabolism in order to investigate the role of lipoxygenase metabolites in the pathogenesis of traumatic shock (LD₉₀). The following inhibitors were used: CGS-5391B (2.5 mg/kg), a cyclooxygenase and lipoxygenase inhibitor, CGS-5677 (2.0 mg/kg), a selective lipoxygenase inhibitor, and U-60, 257 (0.3 mg/kg), a putative inhibitor of glutathione-s-transferase. These inhibitors did not alter arterial blood pressure or heart rate when given to sham shock rats. The traumatic shock model was characterized by a 4.5-fold increase in plasma cathepsin D activity, a 4-fold increase in plasma myocardial depressant factor (MDF) activity, and a mean survival time of 1.5 ± 0.2 h. Only the dual inhibitor significantly blunted the accumulation of cathepsin D in the plasma (7.5 ± 0.8 vs 11.3 ± 0.8 U/ml, p<0.01). However, all three inhibitors significantly suppressed plasma MDF accumulation by 50–60%: CGS-5391B, CGS-5677, and U-60,2257 (p<0.01). Moreover, these three agents significantly improved survival time in traumatic shock. The increased survival time and reduced MDF activity afforded by these inhibitors suggest a significant role for lipoxygenase metabolites, particularly LTC₄ and LTD₄, in the pathogenesis of traumatic shock.