Valine occurrence

An MAA with a possible restricted geographic occurrence is mycosporine-glycine valine. This MAA was first described from a survey of Antarctic species and was initially observed only in consumer organisms (invertebrates and fish), not any of the sampled primary producers.107 Subsequent studies in the Antarctic have identified this MAA in the diatom Fragilariopsis cylindrus, the haptophyte Phaeocystis sp., and mixed assemblages of Southern Ocean phytoplankton.124 126 128 There have been a few tentative identifications of mycosporine-glycine valine in organisms from... 

Subsequently, shallow water collections of Lyngbya majuscula from Puerto Rico and the Dry Tortugas yielded additional supplies of ATX as well as a new congener termed antillatoxin B (Figure 6.10) [149]. The structure of the new metabolite was determined largely by comparison with the spectroscopic data set for ATX, and stereochemistry deduced by Marfey s analysis for L-alanine while the i-N-methyl homophenylalanine was proposed based on nuclear Overhauser effect (nOe) and bioassay results. Substitution of i-N-methyl homo-phenylalanine, an intriguing amino acid of quite rare occurrence in natural products, for i-N-methyl valine... 

The co-occurrence of these three methoxypyrazines is consistent with a biosynthetic pathway (Figure 2) proposed over 20 years ago 14), The amino acid leucine is envisaged as the source of the C4 side chain of the methoxypyrazine, through condensation of its amino amide with an unspecified C2 component, and methylation of the initial pyrazinone condensation product. This proposed biosynthetic pathway readily accommodates all three methoxypyrazines through incorporation of either leucine, isoleucine or valine, all of which are commonly available amino acids in plants. Although the validity of this pathway in vines or other plant material is unknown, the major features of this proposed pathway have been shown to apply to the biosynthesis of isopropylmethoxypyrazine by certain bacteria (75, 16). 

The latter point to the natural occurrence of betaxanthins derived from a-ami-noadipic acid, asparagine, leucine, and valine. Some of these pigments were prepared from betalamic acid and the corresponding amino acids 71). 

How does the amino acid sequence of a protein specify its three-dimensional structure How does an unfolded polypeptide chain acquire the form of the native protein These fundamental questions in biochemistry can be approached by first asking a simpler one What determines whether a particular sequence in a protein forms an a helix, a (3 strand, or a turn One source of insight is to examine the frequency of occurrence of particular amino acid residues in these secondary structures (Table 2.3). Residues such as alanine, glutamate, and leucine tend to be present in a helices, whereas valine and isoleucine tend to be present in (3 strands. Glycine, asparagine, and proline have a propensity for being present in turns. 

Occurrence trace component in many essential oils and foods. Important, e.g., in butter, cheese, whisky, bread, coffee flavor and black currants (see fruit flavors). It is formed as by-product in the biosyntheses of leucine and l-valine and in the metabolism of lactic bacteria. 

Spencer, K. C., and D. S. Seigler, Co-occurrence of valine/isoleucine-derived and cyclopentenoid cyanogens in a Passiflora species, Biochem. Syst. Ecol., 13, 303-304 (1985e). 

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