Isoleucine

Abstract: A statistical analysis shows that the aliphatic index, which is defined as the relative volume of a protein occupied by aliphatic side chains (alanine, valine, isoleucine, and leucine), of proteins of thermophilic bacteria is significantly higher than that of ordinary proteins. The index may be regarded as a positive factor for the increase of thermostability of globular proteins.

Abstract: To study the relationship between the primary structure of transforming growth factor alpha (TGF-alpha) and some of its functional properties (competition with epidermal growth factor (EGF) for binding to the EGF receptor and induction of anchorage-independent growth), we introduced single amino acid mutations into the sequence for the fully processed, 50-amino-acid human TGF-alpha. The wild-type and mutant proteins were expressed in a vector by using a yeast alpha mating pheromone promoter. Mutations of two amino acids that are conserved in the family of the EGF-like peptides and are located in the carboxy-terminal part of TGF-alpha resulted in different biological effects. When aspartic acid 47 was mutated to alanine or asparagine, biological activity was retained; in contrast, substitutions of this residue with serine or glutamic acid generated mutants with reduced binding and colony-forming capacities. When leucine 48 was mutated to alanine, a complete loss of binding and colony-forming abilities resulted; mutation of leucine 48 to isoleucine or methionine resulted in very low activities. Our data suggest that these two adjacent conserved amino acids in positions 47 and 48 play different roles in defining the structure and/or biological activity of TGF-alpha and that the carboxy terminus of TGF-alpha is involved in interactions with cellular TGF-alpha receptors. The side chain of leucine 48 appears to be crucial either indirectly in determining the biologically active conformation of TGF-alpha or directly in the molecular recognition of TGF-alpha by its receptor.

Abstract: Incorporation of radiolabeled precursors into muscle proteins was studied in isolated rat hemidiaphragms. A mixture of three branched-chain amino acids (0.3 mM each) added to media containing glucose stimulated the incorporation of [14C]lysine into proteins. When tested separately, valine was ineffective, isoleucine was inhibitory, but 0.5 mM leucine increased the specific activity of muscle proteins during incubation with [14C]lysine or [14C]acetate in hemidiaphragms from fed or fasted rats incubated with or without insulin. Preincubation with 0.5 mM leucine increased the specific activity of muscle proteins during a subsequent 30- or 60-min incubation with [14C]lysine or [14C]pyruvate without leucine. Preincubation with other amino acids (glutamate, histidine, methionine, phenylalanine, or tryptophan) did not exert this effect. When hemidiaphragms were incubated with a mixture of amino acids at concentrations found in rat serum and a [14C]lysine tracer, the specific activity of muscle proteins increased when leucine in the medium was raised from 0.1 to 0.5 mM. Experiments with actinomycin D and cycloheximide suggested that neither RNA synthesis nor protein synthesis are required for the initiation of the leucine effect. Leucine was not effective when added after 1 h preincubation without leucine. The concentration of lysine in the tissue water of diaphragms decreased during incubation with 0.5 mM leucine in the presence or absence of cycloheximide, suggesting that leucine inhibited protein degradation. During incubation with [3h]tyrosine (0.35 mM) the addition of 0.5 mM leucine increased the specific activity of muscle proteins, while the specific activity of intracellular tyrosine remained constant and its concentration decreased, suggesting that leucine also promoted protein synthesis. The concentration of leucine in muscle cells or a compartment thereof may play a role in regulating the turnover of muscle proteins and influence the transition to negative nitrogen balance during fasting, uncontrolled diabetes, and the posttraumatic state. Leucine may play a pivotal role in the protein-sparing effect of amino aicds.

Abstract: Nitrogen metabolism in higher plants the enzymes of glutamine, glutamate, asparagine and aspartate metabolism seine and glycine metabolism in higher plants the shikmate pathway the biosynthesis of tryptophan, tyrosine and phenyalanine from chorismate lysine, threonine and methionine biosynthesis biosynthesis of valine, leucine, and isoleucine regulation of proline and arginine biosynthesis in plants biosynthesis of cysteine histine biosynthesis amino acid transport role of amino acides in abiotic satress resistance inhibitors of tryptophan, phenylalanine and tyrosine biosynthesis as herbicides inhibotors of histidine biosynthesis inhibitors of glutamine biosynthesis herbicide-resistant crops to inhibitors of amino acid biosynthesis enhancing the content of the essential amnio acids lysine and thereonine in plants methionine enhancement in plants glucosinolates biosynthesis of cyanogenic glycosides, cyanolipids, and related compounds.