Protein synthesis enzymes

The thyroid gland secretes two hormones that regulate protein synthesis, enzyme activity, and stimulate mitochondrial oxidation. These are thyroxine (T4) and triiodothyronine (T3). The thyroid gland secretes 20% of the circulating T3. The remaining 80% comes from degradation of T4 hormone. Approximately 40% of T4 is degraded and becomes T3. 

Chemical and physical structure, together with mobility or flexibility of chain segments and molecules, determine the properties and applications of synthetic and natural macromolecules. The chemical structure of the macromolecule influences its reactivity the physical structure, however, determines its material properties. Nucleic acids, for example, carry genetic information and/or act as matrices for protein synthesis. Enzymes are very specific catalysts. With synthetic polymers, on the other hand, the chemical properties... 

Although a great deal is still unknown regarding the roles of phenolic acids in plants, they have been connected with diverse functimis, including nutrient uptake, protein synthesis, enzyme activity, photosynthesis, stmctural components, and allelopathy [17]. 

The mechanisms that regulate protein biosynthesis must be such that appropriate concentrations and types of enzymes can be synthesized in response to extracellular conditions. Furthermore, the protein biosynthetic mechanism is of such paramount importance to life, and so complex, that we would expect multiple controls to exist. This expectation is completely justified—such controls being found at all levels of information transfer required in the protein biosynthetic mechanism. In order to maintain a balance between the component parts, the regulatory mechanisms must control the rates of protein synthesis, utilization, and degradation. Of course, it need hardly be pointed out that, while nucleic acids provide the information for protein synthesis, enzymes mediate the biosynthetic processes themselves. 

Mutations in the regulatory genes usually produce dramatic results. A mutant repressor gene may produce a defective protein which cannot bind to the operator and would result in continued protein synthesis. Enzymes which, in normal cells, are inducible thus become constitutive. Constitutive operator mutants also occur where an altered base sequence in the DNA of the operator region results in loss of the ability to bind the normal repressor protein. 

Metabolic Functions. The functions of the thyroid hormones and thus of iodine are control of energy transductions (121). These hormones increase oxygen consumption and basal metaboHc rate by accelerating reactions in nearly all cells of the body. A part of this effect is attributed to increase in activity of many enzymes. Additionally, protein synthesis is affected by the thyroid hormones (121,122). 

Potassium is required for enzyme activity in a few special cases, the most widely studied example of which is the enzyme pymvate kinase. In plants it is required for protein and starch synthesis. Potassium is also involved in water and nutrient transport within and into the plant, and has a role in photosynthesis. Although sodium and potassium are similar in their inorganic chemical behavior, these ions are different in their physiological activities. In fact, their functions are often mutually antagonistic. For example, increases both the respiration rate in muscle tissue and the rate of protein synthesis, whereas inhibits both processes (42). 

Puromycin. Puromycin (19), elaborated by S. alboniger (1—4), inhibits protein synthesis by replacing aminoacyl-tRNA at the A-site of peptidyltransferase (48,49). Photosensitive analogues of (19) have been used to label the A-site proteins of peptidyltransferase and tRNA (30). Compound (19), and its carbocycHc analogue have been used to study the accumulation of glycoprotein-derived free sialooligosaccharides, accumulation of mRNA, methylase activity, enzyme transport, rat embryo development, the acceptor site of human placental 80S ribosomes, and gene expression in mammalian cells (51—60). 

A different kind of enzyme, translocase [80700-39-6], which transfers a fragment of NAD to the protein—synthesis factor (elongation factor 2), is catalyzed by diphtheria toxin, thereby inhibiting protein synthesis (43). In tumor cells, the rate of protein synthesis is 100 to 1000 times more sensitive to diphtheria toxin than the analogous process in normal cells (41) therefore, diphtheria toxin is selectively toxic to tumor cells. 

The field of synthetic enzyme models encompasses attempts to prepare enzymelike functional macromolecules by chemical synthesis [30]. One particularly relevant approach to such enzyme mimics concerns dendrimers, which are treelike synthetic macromolecules with a globular shape similar to a folded protein, and useful in a range of applications including catalysis [31]. Peptide dendrimers, which, like proteins, are composed of amino acids, are particularly well suited as mimics for proteins and enzymes [32]. These dendrimers can be prepared using combinatorial chemistry methods on solid support [33], similar to those used in the context of catalyst and ligand discovery programs in chemistry [34]. Peptide dendrimers used multivalency effects at the dendrimer surface to trigger cooperativity between amino acids, as has been observed in various esterase enzyme models [35]. 

The shift in pattern of protein synthesis during anaerobiosis has been observed in root tissue of many other plant species including rice, sorghum, barley, pea, and carrot (see Sachs Ho, 1986). In anaerobically treated barley aleurone cells, lactate dehydrogenase (LDH) activity increases (Hanson Jacobsen, 1984) as does enzyme activity and mRNA levels for ADH (Hanson, Jacobsen Zwar, 1984). 

The membranes of the endoplasmic reticulum contain the enzyme system for acylglycerol synthesis, and the ribosomes are responsible for protein synthesis. 

Pathways are compartmentalized within the cell. Glycolysis, glycogenesis, glycogenolysis, the pentose phosphate pathway, and fipogenesis occur in the cytosol. The mitochondrion contains the enzymes of the citric acid cycle, P-oxidation of fatty acids, and of oxidative phosphorylation. The endoplasmic reticulum also contains the enzymes for many other processes, including protein synthesis, glycerofipid formation, and dmg metabolism. 

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