The interplay o light and heat in bleaching rhodopsin

Rhodopsin, the pigment of the retinal rods, can be bleached either by light or by high temperature. Earlier work had shown that when white light is used the bleaching rate does not depend on temperature, and so must be independent of the internal energy of the molecule. On the other hand thermal bleaching in the dark has a high temperature dependence from which one can calculate that the reaction has an apparent activation energy of 44 kg. cal. per mole. It has now been shown that the bleaching rate of rhodopsin becomes temperature-dependent in red light, indicating that light and heat cooperate in activating the molecule. Apparently thermal energy is needed for bleaching at long wave lengths where the quanta are not sufficiently energy-rich to bring about bleaching by themselves. The temperature dependence appears at 590 mµ. This is the longest wave length at which bleaching by light proceeds without thermal activation, and corresponds to a quantum energy of 48.5 kg. cal. per mole. This value of the minimum energy to bleach rhodopsin by light alone is in agreement with the activation energy of thermal bleaching in the dark. At wave lengths between 590 and 750 mµ, the longest wave length at which the bleaching rate was fast enough to study, the sum of the quantum energy and of the activation energy calculated from the temperature coefficients remains between 44 and 48.5 kg. cal. This result shows that in red light the energy deficit of the quanta can be made up by a contribution of thermal energy from the internal degrees of freedom of the rhodopsin molecule. The absorption spectrum of rhodopsin, which is not markedly temperature-dependent at shorter wave lengths, also becomes temperature-dependent in red light of wave lengths longer than about 570 to 590 mµ. The temperature dependence of the bleaching rate is at least partly accounted for by the temperature coefficient of absorption. There is some evidence that the temperature coefficient of bleaching is somewhat greater than the temperature coefficient of absorption at wave lengths longer than 590 mmicro;. This means that the thermal energy of the molecule is a more critical factor in bleaching than in absorption. It shows that some of the molecules which absorb energy-deficient quanta of red light are unable to supply the thermal component of the activation energy needed for bleaching, so bringing about a fall in the quantum efficiency. The experiments show that there is a gradual transition between the activation of rhodopsin by light and the activation by internal energy. It is suggested that energy can move freely between the prosthetic group and the protein moiety of the molecule. In this way a part of the large amount of energy in the internal degrees of freedom of rhodopsin could become available to assist in thermal activation. Assuming that the minimum energy required for bleaching is 48.5 kg. cal., an equation familiar in the study of unimolecular reaction has been used to estimate the number of internal degrees of freedom, n, involved in supplying the thermal component of the activation energy when rhodopsin is bleached in red light. It was found that n increases from 2 at 590 mµ to a minimum value of 15 at 750 mµ. One wonders what value n has at 1050 mµ, where vision still persists, and where rhodopsin molecules may supply some 16 kg. cal. of thermal energy per mole in order to make up for the energy deficit of the quanta.     

Multiple Feedbacks Contribute to a Centennial Legacy of Reindeer on Tundra Vegetation

Historical contingency is the impact of past events, like the timing and order of species arrival, on community assembly, and can sometimes result in alternative stable states of ecological communities. Large herbivores, wild and domestic, can cause profound changes in the structure and functioning of plant communities and therefore probably influence historical contingency; however, little empirical data on the stability of such shifts or subsequent drivers of stability are available. We studied the centennial legacy of reindeer (Rangifer tarandus) pressure on arctic tundra vegetation by considering historical milking grounds (HMGs): graminoid- and forb-dominated patches amid shrub-dominated tundra, formed by historical Sami reindeer herding practices that ended approximately 100 years ago. Our results show that the core areas of all studied HMGs remained strikingly stable, being hardly invaded by surrounding shrubs. Soil nitrogen concentrations were comparable to heavily grazed areas. However, the HMGs are slowly being reinvaded by vegetative growth of shrubs at the edges, and the rate of ingrowth increased with higher mineral N availability. Furthermore, our data indicate that several biotic feedbacks contribute to the stability of the HMGs: increased nutrient turnover supporting herbaceous vegetation, strong interspecific competition preventing invasion and herbivore damage to invading shrubs. In particular, voles and lemmings appear to be important, selectively damaging shrubs in the HMGs. We concluded that HMGs provide clear evidence for historical contingency of herbivore effects in arctic ecosystems. We showed that several biotic feedbacks can contribute to subsequent vegetation stability, but their relative importance will vary in time and space.     

What Is the Future for Zoos and Aquariums?

ABSTRACT

Animal welfare concerns have plagued the professional zoo and aquarium field for decades. Societal differences remain concerning the well-being of animals, but it appears a shift is emerging. Scientific studies of animal welfare have dramatically increased, establishing that many previous concerns were not misguided public empathy or anthropomorphism. As a result, both zoo and aquarium animal welfare policy and science are now at the center of attention within the world’s professional zoos and aquariums. It is now possible to view a future that embraces the well-being of individual captive exotic animals, as well as that of their species, and one in which professional zoos and aquariums are dedicated equally to advancing both. Though the ethics of keeping exotic animals and animals from the wild in captivity are still a contentious subject both outside and even within the profession, this study argues. We argue that this path forward will substantially improve most zoo and aquarium animals' welfare and could significantly reduce societal concerns. If animal welfare science and policy are strongly rooted in compassion and embedded in robust accreditation systems, the basic zoo/aquarium paradigm will move toward a more thoughtful approach to the interface between visitors and animals. It starts with a fundamental commitment to the welfare of individual animals.     

THE EFFECT OF SOME BEVERAGES ON THE PERCEPTION OF SUCCEEDING BASIC TASTES

The objective of this study was to investigate the effect beverages have on subsequently perceived basic tastes. Two types of milk, Cola and water were used to rinse the mouth prior to conducting a Time Intensity study with basic taste solutions. From this some effects of the prior beverage onto the TI parameters was found. Especially Cola showed an effect on the intensity of the subsequently tasted sweet taste, and whole milk showed a stronger effect than skim milk. The effects showed both in size and timing of the basic taste intensities.     

Intracellular Distribution of 5' Nucleotidase in Rat Liver

The intracellular distribution of 5' nucleotidase was investigated in rat liver by biochemical analysis of cell fractions obtained by differential centrifugation. The enzymatic activity was measured by determination of the inorganic phosphorus liberated from 5' nucleotides. The 5' nucleotidase activity was mainly found in the nuclear and microsomal fractions. An attempt to extract the enzyme from these fractions with Mg⁺⁺ ion solutions was unsuccessful. It is concluded that 5' nucleotidase is actually present in the nuclear and microsomal fractions of rat liver cells.     

Production of a diagnostic monoclonal antibody in perennial alfalfa plants.

The increasing use of monoclonal antibodies (mAbs) in diagnostic reagents necessitates efficient and cost-effective mAb production methods. In blood banks, one of the most routinely used reagents is the anti-human IgG reagent used for the detection of non-agglutinating antibodies. Here we report the production of a functional, purified anti-human IgG, through the expression of its encoding genes in perennial transgenic alfalfa. Transgenic plants expressing the light- and heavy-chain encoding mRNAs were obtained, and plants from crosses were found to express fully assembled C5-1. The purification procedure yielded mainly the H2L2 form with specificity and affinity identical to those of hybridoma-derived C5-1. The ability to accumulate the antibody was maintained both in parental F1 lines during repeated harvesting and in clonal material; the antibody was stable in the drying hay as in extracts made in pure water. Also, plant and hybridoma-derived C5-1 had similar in vivo half-lives in mice. These results indicate that plant C5-1 could be used in a diagnostic reagent as effectively as hybridoma-derived C5-1, and demonstrates the usefulness of perennial systems for the cost-effective, stable, and reliable production of large amounts of mAbs.     

cGMP and cAMP cause pulmonary vasoconstriction in the presence of hemolysate.

We recently reported that addition of a small amount of hemolysate to the salt solution that perfused isolated rat lungs hypersensitized the vasculature to subsequent additions of ANG II or exposure to hypoxia, and addition of NO gas (. NO) to the perfusate that contained hemolysate caused a strong vasoconstrictor rather than a vasodilator response. In the present study, we demonstrate that CO and the secondary messengers cGMP and cAMP (usually associated with vasodilation) exert similar effects in hemolysate-perfused lungs. Analogs of the cyclic nucleotides cGMP or cAMP (8-bromo-cGMP and dibutyryl-cAMP, respectively) caused profound vasoconstriction in the isolated rat lung perfused with a salt solution that contained hemolysate. The cGMP- or cAMP-analog-induced vasoconstriction was inhibited by chemically dissimilar Ca2+ antagonists, by the protein phosphatase inhibitor okadaic acid, and, to a lesser degree, by protein kinase inhibitor H-7. Antiphosphothreonine immunoblotting demonstrated that lungs perfused with hemolysate exhibit increased phosphorylation of several proteins. These data indicate that, in the presence of hemolysate, pulmonary vasculature responds to nominally vasodilatory stimuli, including analogs of cGMP and cAMP, with vasoconstriction rather than vasodilation. The importance of our finding is the paradoxical nature of the response to (analogs of) cyclic nucleotides because, to our knowledge, cyclic nucleotide-induced vasoconstriction has not been previously reported.