CATECHOLAMINE-CONTAINING PROTEINS FROM THE PHARATE PUPAL CUTICLE OF THE TOBACCO HORNWORM, MANDUCA-SEXTA

Three catecholamine-containing proteins from tanning, pharate pupal, a bdominal cuticle of the tobacco hornworm, Manduca sexta, have been pur ified to apparent homogeneity and characterized, These proteins have a pparent molecular masses of 32, 41 and 48 kDa and were shown by liquid chromatography-electrochemical analysis, after heating in 1 M acetic acid at 110 degrees C, to release N-beta-alanylnorepinephrine (NBANE), NBANE is a hydrolysis product of N-beta-alanyldopamine (NBAD) that is bonded covalently at the beta-side-chain carbon to amino acid residue s of cuticular proteins, Amino acid compositional analysis revealed th at MS-PCP32 (32 kDa) has a high content of alanine (25.6%), valine (13 .1%), proline (10.8%) and glycine (10%), a low level of phenylalanine, and no detectable tyrosine or methionine. In contrast, MS-PCP41 (41 k Da) had a much higher content of glycine (31.2%) and substantial level s of serine (9.2%), proline (10.2%) and glutamate/glutamine (10.6%), w hereas tyrosine and phenylalanine were not detected, Two of the three purified proteins showed apparent similarities to each other in N-term inal amino acid sequences, and to several other known insect cuticular proteins, Proteins MS-PCP41 and MS-PCP48 had the characteristic GGX t riplet repeat, which is found in a variety of cuticular proteins and m ay be important for protein folding appropriate for cuticular function s, Therefore, a diversity of cuticular proteins with different amino a cid sequences and properties apparently are secreted into the presumpt ive pupal exocuticle. These then can form adducts and possible cross-l inks with NBAD through its quinonoid intermediates during cuticular sc lerotization. Published by Elsevier Science Ltd.