Isoleucine chemical structure

Chemical structure. The structure of the free base of Cypridina luciferin (C22H27ON7, Mr 405.50) was determined by Kishi et al. (1966a,b) as shown below (A) its sec-butyl group is in the same configuration as in L-isoleucine. The structure of oxyluciferin reported by the same authors contained an error, and the structure was corrected later as shown in Fig. 3.1.8 (McCapra and Chang, 1967 Stone, 1968). 

T. Kohno, D. Kohda, M. Haruki, S. Yokoyama, and T. Miyazawa, Non-protein amino acid furanomycin, unlike isoleucine in chemical structure, is changed to isoleucine tRNA by isoleucyl-tRNA synthetase and incorporated into protein. J. Biol. 

Figure 7.10 Chemical structure of SB-234764, a tight binding bisubstrate inhibitor of bacterial isoleucine tRNA synthetase.

It was snbseqnently discovered that the first enzyme in the pathway for isoleucine synthesis, which is threonine deaminase, was inhibited by isoleucine in an extract of E. coli. No other amino acid caused inhibition of the enzyme. Threonine deaminase is, in fact, the rate-limiting enzyme in the pathway for isoleucine synthesis, so that this was interpreted as a feedback control mechanism (Fignre 3.13(a)). Similarly it was shown that the hrst enzyme in the pathway for cytidine triphosphate synthesis, which is aspartate transcarbamoylase, was inhibited by cytidine triphosphate (Fignre 3.13(b)). Since the chemical structures of isoleucine and threonine, or cytidine triphosphate and aspartate, are completely different, the qnestion arose, how does isolencine or cytidine triphosphate inhibit its respective enzyme The answer was provided in 1963, by Monod, Changenx Jacob. 

Although leucine and isoleucine have different chemical structures (see below), they have the same atomic composition so their mass is the same and the mass spectrometer sees them as the same. 

We have shown in the last topic that a triplet code with four letters (DNA/RNA bases) to choose from is mathematically sufficient to encode 20 amino acids, but is it structurally sufficient What is there about a set of three nucleotide bases that enables it to recognise and specify the very different chemical structure of a single amino acid Likewise, how can very similar codons specify very different amino acids. How is it that AUG can specify methionine while, with only one base different in each case, AAG specifies lysine, GUG specifies valine, AUC specifies isoleucine The answer to this puzzle lies, as so often, in the properties of a remarkable set of enzyme proteins and a matching set of RNA molecules called transfer RNA (tRNA), which together provide, in effect, an adaptor kit. 

Figure 4.7 Chemical structures of the amino acids L- //o-isoleucine (L-aiLe), D-leucine (D-Leu), L-norvaline (L-Nva), D-methionine (D-Met), L-2-aminobutyric acid (L-Abu) and D-norleucine (D-Nle).

The sulfonylurea herbicides are a new family of chemical compounds, some of which are selectively toxic to weeds but not to crops. The selectivity of the sulfonylureas results from their metabolism to non-toxic compounds by particular crops, but not by weeds. In addition to efficient weed control, the sulfonylurea herbicides provide environmentally desirable properties such as field use rates as low as two grams/hectare and very low toxicity to mammals. The high specificity of the herbicides for their molecular target contributes to both of these properties. In addition, the low toxicity to mammals results from their lack of the target enzyme for the herbicides. Sulfonylureas inhibit the enzyme acetolactate synthase (ALS), also known as acetohydroxyacid synthase (AHAS), which catalyzes the first common step in the biosynthesis of the branched chain amino acids leucine, isoleucine and valine. In mammals these are three of the essential amino acids which must be obtained through dietary intake because the biosynthetic pathway for the branched chain amino acids is not present. The prototype structure of a sulfonylurea herbicide is shown in Figure 1. 

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