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The 2.80 +/- 0.20 mumol of anions found/mg of isolated and purified dry nematocysts (capsular secretory products of stinging cells) from Hydra make up the majority of the soluble capsular content. They are, in cooperation with corresponding cations, responsible for the generation and regulation of an internal osmotic pressure that amounts up to 150 bar (Weber, J. (1989) Eur. J. Biochem. 184, 465-476). The anions are organized as linear homopolymers of L-glutamic acids which are linked by gamma-carboxyl-alpha-amino amide bonds; the degree of polymerization is heterogeneous and dependent on the particular type of nematocyst. In situ the intracapsular glutamic acid monomer concentration is as high as 2 M. This is the first time that poly(gamma-glutamic acid)s, which are known to occur in some selected bacteria, are reported for eucaryotes. It is suggested that they may also be present as predominant components in nematocysts of other cnidarian species and thus might represent a class of compounds which is characteristic for a whole phylum of the animal kingdom.
Juliane Weber (Fri,) studied this question.