ISOFORMS OF A CUTICULAR PROTEIN FROM LARVAE OF THE MEAL BEETLE, TENEBRIO-MOLITOR, STUDIED BY MASS-SPECTROMETRY IN COMBINATION WITH EDMAN DEGRADATION AND 2-DIMENSIONAL POLYACRYLAMIDE-GEL ELECTROPHORESIS

Simultaneous sequencing, using a combination of mass spectrometry and Edman degradation, of three approximately 15-kDa variants of a cuticul ar protein extracted from the meal beetle Tenebrio molitor larva is de monstrated. The information obtained by matrix-assisted laser desorpti on ionization mass spectrometry (MALDI MS) time-course monitoring of e nzymatic digests was found essential to identify the differences among the three variants and for alignment of the peptides in the sequence. To determine whether each individual insect larva contains all three protein variants, proteins extracted from single animals were separate d by two-dimensional gel electrophoresis, electroeluted from the gel s pots, and analyzed by MALDI MS. Molecular weights of the proteins pres ent in each sample could be obtained, and mass spectrometric mapping o f the peptides after digestion with trypsin gave additional informatio n. The protein isoforms were found to be allelic variants.