Importance Of Different Pathways Research Articles

Zinc Regulation in the LobsterHomarus Gammarus:Importance of Different Pathways of Absorption and Excretion

Zinc is one of the most important of the essential trace metals and more than 90 zinc-containing enymes and proteins have been discovered: furthermore, zinc increases the activity of many other enzymes (Vallee, 1978). It is not surprising, therefore, that in some groups of animals the body concentration is regulated against fluctuations in intake. Decapod crustaceans comprise one such group, although the ways in which regulation is achieved vary from species to species. In the freshwater crayfish,Austropotamobius pallipes, excretion in the faeces is a major pathway for removing zinc (Bryan, 1967a) whereas in the shore crabCarcinus maenaslosses over the body surface also assume considerable importance (Bryan, 1966). On the other hand, preliminary work on the lobsterHomarus gammarus(formerlyH. vulgaris) suggests that in this species urinary excretion plays a major role in regulation (Bryan, 1964). The present work continues the study of zinc regulation in lobsters and its main aims are: (1) to measure rates of absorption from sea water over a wide range of concentrations and study the uptake mechanism; (2) to examine absorption from the stomach under different conditions; (3) to determine the relative importance of different pathways for the removal of zinc in response to various levels of intake.

Diffusional support of arteries.

The relative role of the arterial lumen, adventitial vasa vasorum, and medial vasa vasorum in nutritional support of arteries is unclear. We have used a newly developed autoradiographic method to study diffusion of metabolically inert [14C]antipyrine into arteries to determine the relative importance of different pathways in nutritional support of arteries. [14C]antipyrine was homogenously distributed across the media of small arteries within 15 s, which indicates that diffusion into the central media was rapid. In the thoracic and abdominal aorta, levels of antipyrine were higher in the inner media (P less than 0.05) than in the middle of the media. Levels of antipyrine in outer media of the thoracic aorta (which has medial and adventitial vasa) were comparable to those observed in the inner media, but antipyrine levels were lower in outer than in inner media of the abdominal aorta (which has adventitial vasa only). Ligation of intercostal arteries, which are the source of medial vasa vasorum in the thoracic aorta, decreased diffusional support to the outer media of the thoracic aorta. We conclude that 1) diffusional support is more effective in thinner muscular arteries than in the aorta, 2) both luminal and abluminal sources of nutrition are important, particularly for the aorta, 3) vasa vasorum appear to be important for adequate diffusional support of the thoracic aortic media, and 4) medial vasa vasorum may be more effective than adventitial vasa vasorum in nourishing the aorta.

Potential impact of size-selective planktivory on phosphorus release by zooplankton

A laboratory model of phosphorus release by Daphnia rosea was implemented for published zooplankton data from lakes characterized by different abundances of size-selective planktivores. Size-selective feeding reduces average prey size and increases P release per unit biomass. At the system level, decreased prey standing crop associated with higher planktivore abundance could balance the size dependent increase in P release rate. However, estimates of both net reduction and net increase in rate of P release from zooplankton resulted from model application. Size-selective feeding might be important not only in energetic or evolutionary relationships between predator and prey but also in determination of the relative importance of different pathways of phosphorus flow through pelagic systems.

Cuprous complexes and dioxygen. VIII. Steric factors controlling one‐ or two‐electron reduction of O2 by cuprous complexes with substituted imidazoles

AbstractIn aqueous acetonitrile (AN), Cu (I) forms the complexes Cu(AN)L+ and CuL with a series of substituted imidazoles (L). Stability constants logK of Cu(AN)+ + L ⇌ Cu(AN)L+ and logβ2 were near 5 and 12, resp., log units for all ligands. The rate of autoxidation is described by −d[O2]/dt=[CuL]2[O2](ka/(1+kb[CuL]) + (kc[L]+kd)/([CuL] + ke[Cu])), implying competition between one‐ or two‐electron reduction of O2. The value of kc decreases from 5500M−2S−1 for unsubstituted imidazole to about 40M−2S−1 for 2‐methylimidazole or 1,2‐dimethyl‐imidazole and essentially zero for the corresponding 2‐ethyl‐derivatives. On the other hand, ka and kb are much less influenced by the nature of the ligands, all values being near 5 · 104M−2S−1 and 103M−1, respectively, for the complexes with the last four bases. Thus rather subtle sterical changes may strongly influence the relative importance of different pathways in the reduction of dioxygen by cuprous complexes.

MOLECULAR BIOLOGY TECHNIQUES INVOLVED IN ENVIRONMENTAL MONITORING

A short review of the main molecular methods recently involved in monitoring
 environmental pollution is the aim of our aper. The elimination of a wide range of pollutants and wastes from the
 environment is an absolute requirement to promote a sustainable development of our society with low environmental impact. New methodological breakthroughs in sequencing, genomics, proteomics, bioinformatics and imaging are producing vast amounts of information. Functional genomic and metagenomic approaches will
 increase our understanding of the relative importance of different pathways and regulatory networks to carbon
 flux in particular environments and for particular compounds, and they will certainly accelerate the development of bioremediation technologies and biotransformation processes. Tools for in situ monitoring of environmental pollutants are destined for both aims providing early warning systems and conceiving more efficient and less expensive remediation treatments.