Three storage proteins named SL-1, SL-2 and SL-3, the former two being synthesized only in the last larval instar, were purified from haemolymph of the common cutworm, Spodoptera litura. All three storage proteins have molecular sizes between 400 and 450 kDa, and are composed of subunit(s) which range in size from 70 to 80 kDa. Chemical cross-linking confirmed that these storage proteins are hexamers. SL-1 and -2 are basic proteins showing homogeneous amino acid compositions with c. 10% aromatic amino acids, the former being rich in methionine. Both are cross-reactive to antiserum against SP-1 (methionine-rich storage protein) of Bombyx mori at the native molecular level, but only SL-1 is cross-reaction to it at the polypeptide level. SL-3 is a neutral protein with an amino acid composition that differs considerably from those of SL-1 and -2, having 20% aromatic amino acids. It is cross-reactive only to antiserum against SP-2 (arylphorin) of B. mori, both at native and subunit molecular levels. From these results, it was concluded that SL-1 and -2 are 'methionine-rich' storage proteins with similar conformations but with different epitopes in subunit molecules, while SL-3 is an arylphorin. © 1994.
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