FURTHER OBSERVATIONS ON THE FINE STRUCTURE OF THE PARIETAL EYE OF LIZARDS

An electron microscopical study of the third eye of the Western Fence Lizard, Sceloporus occidentalis, fixed with 1 per cent osmium tetroxide, pH 7.4–7.6, for 16 to 20 hours at 0°C., revealed the following new facts. The fibrillar system of the retinal photoreceptor consists of nine double fibrils enclosed in a sheath. Pigment cells and lens cells possess similar systems. Two short cylindrical centrioles are associated with the fibrillar apparatus: one, from which striated rootlets extend inward, lies at the base of the fibrils, with the other at an oblique angle to the axis of the system. A Golgi complex, whorls of endoplasmic reticulum, lipid (?) droplets, and other organelles and inclusions in the photoreceptors are described. An axon leads from the base of the photoreceptor into the nervous layer of the retina which consists of many nerve fibers and large ganglion cells. Although the pattern of neural connections has not yet been determined, some synapses were found. The parietal nerve consists of about 250 non-medullated fibers. The capsule of the eye usually has a layer of iridocytes, which contain rows of guanine (?) rods. A few parietal eyes of the Granite Night Lizard, Xantusia henshawi, were also examined. Large lipid (?) droplets occur in the bases of their receptoral processes.     

Fine structure of ocelli in larvae of an archiannelid,Polygordius cf. appendiculatus

Summary The ocelli of trochophore and segmented larvae of the archiannelid Polygordius cf. appendiculatus were studied by electron microscopy. An eye consists of two pigmented supportive cells forming an eyecup that encloses one sensory cell bearing one (trochophore) or two (segmented larva) ranks of microvilli and one adventitious cilium. Remarkably abundant tubules (submicrovillar endoplasmic reticulum) radiate from the perinuclear region of the sensory cell, which lies outside the ocellus, toward its receptoral end. Possible functions of the tubules are proposed: carriers of ions, metabolites and photopigments; pinocytic uptake of products resulting from photoreception; storage of membrane; and light guides. Finally, the eyes of Polygordius larvae are believed to have evolutionary significance and provide further support for Eakin's theory of diphyletic origin of photoreceptors.     

Carbon-13 nuclear magnetic resonance of heme carbonyls. Cytochrome c and carboxymethyl derivatives of cytochrome c.

Carbonyl complexes of horse cytochrome c and various carboxymethylated derivatives have been examined using 13C NMR (carbon-13 nuclear magnetic resonance) spectroscopy. The multiplicity and chemical shift of the 13CO resonance were found to be functions of pH and the extent of alkylation. Correlations have been made among prominent features of the chemical shift titration curves and changes in the environment of the heme. A simple model compatible with the bulk of previous observations has been suggested to account for the several carbonyl resonance peaks and the complex behavior of the chemical shift with changes in pH.     

Water Scarcity in the Andes: A Comparison of Local Perceptions and Observed Climate, Land Use and Socioeconomic Changes

In the Andean region of South America, understanding communities’ water perceptions is particularly important for water management as many rural communities must decide by themselves if and how they will protect their micro-watersheds and distribute their water. In this study we examine how Water User Associations in the Eastern Andes of Colombia perceive water scarcity and the relationship between this perception and observed climate, land use, and demographic changes. Results demonstrate a complex relationship between perceptions and observed changes. On the one hand, observed changes in land cover match perceptions of deforestation as the primary cause of increasing water scarcity. On the other hand, perceptions of climate driven changes in water availability are not reflected in observed precipitation data. Furthermore, water scarcity was perceived in regions where seasonal rainfall variability is higher but not in regions where annual rainfall is lower. We discuss how these results contribute to our understanding of adaptation to climate change and the implications of possible mismatches between environmental changes and local perceptions.     

Formation of a copper specific binding site in non-native states of beta-2-microglobulin

A debilitating complication of long-term hemodialysis is the deposition of beta-2-microglobulin (beta2m) as amyloid plaques in the joint space. We have recently shown that Cu(2+) can be a contributing, if not causal, factor at concentrations encountered during dialysis therapy. The basis for this effect is destabilization and incorporation of beta2m into amyloid fibers upon binding of Cu(2+). In this work, we demonstrate that while beta2m binds Cu(2+) specifically in the native state, it is binding of Cu(2+) by non-native states of beta2m which is responsible for destabilization. Mutagenesis of potential coordinating groups for Cu(2+) shows that native state binding of Cu(2+) is mediated by residues and structures that are different than those which bind in non-native states. An increased affinity for copper by non-native states compared to that of the native state gives rise to overall destabilization. Using mass spectrometry, NMR, and fluorescence techniques, we show that native state binding is localized to H31 and W60 and is highly specific for Cu(2+) over Zn(2+) and Ni(2+). Binding of Cu(2+) in non-native states of beta2m is mediated by residues H13, H51, and H84, but not H31. Although denatured beta2m has characteristics of a globally unfolded state, it nevertheless demonstrates the following strong specificity of binding: Cu(2+) > Zn(2+) > Ni(2+). This requires the existence of a well-defined structure in the unfolded state of this protein. As Cu(2+) effects are reported in many other amyloidoses, e.g., PrP, alpha-synuclein, and Abeta, our results may be extended to the emerging field of divalent ion-associated amyloidosis.