This chapter focuses on the distinctive properties and functions of the plasma—especially of the plasma proteins. The functions of blood plasma itself are so important that this blood plasma cannot be exhausted by any brief list. Because blood is rapidly circulating, it is essential that the volume of the blood and its physical characteristics—such as viscosity—should be suitable for maintaining that circulation. The interchange of hormones between one tissue and another is of necessity, and the plasma is a great highway of travel for these materials from the tissue where they are produced to those other tissues where their action is primarily exerted. The relation of antibodies to blood plasma is again somewhat similar to that of the hormones. These antibodies are produced in the tissues but may exert their protective action either in another tissue or in the plasma itself, when these antibodies are brought into contact with the antigens for which these are specific.
During protein translation, a variety of quality control checks ensure that the resulting polypeptides deviate minimally from their genetic encoding template. Translational fidelity is central in order to preserve the function and integrity of each cell. Correct termination is an important aspect of translational fidelity, and a multitude of mechanisms and players participate in this exquisitely regulated process. This review explores our current understanding of eukaryotic termination by highlighting the roles of the different ribosomal components as well as termination factors and ribosome-associated proteins, such as chaperones.
The aquaporins (AQPs) are small integral membrane proteins that transport water and in some cases small solutes such as glycerol. Physiological roles of the ten or more mammalian AQPs have been proposed based on their expression in epithelial, endothelial and other tissues, their regulation, and in some cases the existence of humans with AQP mutation. Here, the role of AQPs in mammalian physiology is reviewed, based on phenotype analysis of transgenic mouse models of AQP deletion/mutation. Phenotype studies support the predicted roles of AQPs in kidney tubule and microvessel fluid transport for urinary concentrating function, and in fluid-secreting glandular epithelia. The phenotype studies have also shown unexpected roles of AQPs in brain and corneal swelling, in neural signal transduction, in regulation of intracranial and intraocular pressure, and in tumor angiogenesis and cell migration. The water/glycerol-transporting AQPs were found to play unexpected roles in skin hydration and in fat metabolism. However, many phenotype studies were negative, such as normal airway/lung and skeletal muscle function, despite AQP expression, indicating that tissue-specific AQP expression does not indicate physiological significance. The mouse phenotype data suggest that modulators of AQP expression/function may have such wide-ranging clinical applications as diuretics and in the treatment of brain swelling, glaucoma, epilepsy, obesity, and cancer.
