In the pond-culture of prawn, Penaeus japonicus, the soft part of short-necked clam, Tapes japonica, is commonly used as a sole diet and it has been observed that the prawns are attracted intensely by its press-juice²⁾. As a preliminary study for the exploitation of artificial feed mixture, the extracts of the soft part were analyzed for various components in order to identify the attractant and the amino acid composition of its protein was exa-mined.
Hot-water extracts of the homogenized soft part were made to 70% (v/v) concentration of EtOH, and organic acids, nucleotides and their related compounds, the amounts of quaternary ammonium bases and free amino acids before and after hydrolysis were determined on the super-natant. The precipitates were subjected to the determination of glycogen. The residues from hotwater extraction were applied to the analysis of amino acid composition of the protein.
Results obtained are summarized as follows.
1) The content of extractive nitrogen was remarkably higher than that reported so far on the same species⁵⁾²⁴⁾. A marked increase of α-amino nitrogen after acid-hydrolysis was observed (Table 1).
2) Among organic acids, succinic, fumaric and malic acid were detected. The amount of succinic acid, however, was far less than the data of other workers^6)24)25) (Table 2).
3) The presence of a fairly large amount of IMP was recognized, differing from ordinary molluscan muscles²⁶⁾²⁷⁾, and this may be due to the action of enzymes in the internal organs, which were present in our sample. AMP, UMP, ADP, inosine and hypoxanthine were also found (Table 2).
4) Quaternary ammonium bases were surveyed extensively, but only betaine, homarine and combined choline were detected (Table 2).
5) All amino acids except tryptophan were found in free forms. Among them, taurine, glycine, alanine, glutamic acid and arginine were predominant. After acid-hydrolysis, the amount of the amino acids except taurine and acid-labile ones increased considerably (Table 3). Most of the combined amino acids were considered to be brought into the extracts by the effect of heating in extraction (Table 4).
6) The total nitrogen calculated from these results amounted to 97.9% of the extractive nitrogen. Thus, the distribution of nitrogenous constituents in the extracts was elucidated