COMPLETE AMINO-ACID-SEQUENCE OF THE AA6 SUBUNIT OF THE SCORPION ANDROCTONUS-AUSTRALIS HEMOCYANIN DETERMINED BY EDMAN DEGRADATION AND MASS-SPECTROMETRY

The primary structure of the hernocyanin Aa6 subunit from the scorpion Androctonus australis was resolved by using protein sequencing and ma ss spectrometry for analysis of the polypeptide chain and of fragments obtained by CNBr, trypsin, and chymotrypsin cleavage. Due to the high sensitivity of the methodologies used, only a small amount of materia l, less than 1 mg, was consumed. The complete sequence is composed of 626 amino acid residues and the protein is not glycosylated but probab ly phosphorylated at Ser374. Its molecular mass measured by mass spect rometry (71890 +/- 7 Da) is about 30 Da higher than the mass calculate d from the sequence data (71860.1 Da). The origin of this, difference is not clear but could result from minor molecular heterogeneities. Wi thin the chelicerates, the Aa6 subunit of the arachnid A. australis sh ares 405 identical residues with chain e of another arachnid, Eurypelm a californicum, and 399 with chain a of the merostom Tachypleus triden tatus. The degrees of identity between these three subunits, which are known to occupy the same location in the native hemocyanin oligomers, are significantly higher than those existing between the subunits a, d, and e of E. californicum. This favors the hypothesis that gene dupl ications, leading to separate chains in one species, have occurred bef ore the divergence between arachnids and merostoms.