Configuration assignments of the amino acid residues and the presence of N-methyldehydroalanine in toxins from the blue-green alga, Microcystis aeruginosa

Abstract

—The configuration assignment of the α-carbon atom of amino acid residues in four toxin variants from Microcystis aeruginosa have been made by stereospecific enzymic transformations. The relative conformation assignment of the β-carbon atom of β-CH 3-aspartic acid could be made by comparison of the electrophoretic mobility with literature values reported for the authentic compound. The presence of an N-methyldehydroalanine residue, which, due to elimination of methylamine under hydrolytic conditions, previously escaped detection by conventional means, has been confirmed by identification of N-methylalanine in the hydrolysate after reduction of toxin with sodium borohydride.