DIGESTIVE SITES OF DIETARY PROTEINS AND ABSORPTIVE SITES OF AMINO-ACIDS ALONG THE MIDGUT OF THE SILKWORM, BOMBYX-MORI

The present study was conducted to identify where dietary proteins are digested and where the digested amino acids are absorbed in the midgu t of the silkworm, Bombyx mori, Analysis by electrophoresis on SDS-pol yacrylamide gels shows that few of the protein bands existing in the a rtificial diet were found among the contents of the foremost part of t he midgut; instead, this region contained a duster of low molecular pr otein bands, probably proteolytic products from the dietary proteins, This suggests that digestion of dietary proteins has already taken pla ce in the anterior part of the midgut, This result is confirmed by the fact that an extract from the contents of the anterior part of the mi dgut is capable of digesting soybean proteins, a protein source in the artificial diet, as are extracts from the middle and posterior region s, Estimates of the absorption ratio of amino acids in the midguts wer e observed using chromic oxide as a non-absorbed reference substance, Cumulative absorption ratios of all the amino acids, except glycine, i ncreased gradually as the diet proceeded through the midgut, The resul ts suggest that absorption of overall amino acids, free amino acids an d those in the form of digested peptides, takes place throughout the w hole length of the midgut. Copyright (C) 1996 Elsevier Science Ltd