Regional distribution and substrate specificity of digestive enzymes involved in terminal digestion in Musca domestica hind-midguts.

One membrane-bound alpha-glucosidase and two soluble alpha-glucosidases were isolated from homogenates of the hind-midgut, the main digestive region in Musca domestica larvae. The membrane-bound alpha-glucosidase and the low-Mr soluble alpha-glucosidase hydrolyze maltopentaose better than maltose, maltotriose, and maltotetraose, the reverse being true for the high-Mr soluble alpha-glucosidase. A membrane-bound glucoamylase previously described in Musca domestica midgut was shown by gradient centrifugation and dialysis against EDTA to result from the combined action of an amylase and an alpha-glucosidase. The determination of amylase, alpha-glucosidases, soluble and membrane-bound carboxypeptidase A, membrane-bound aminopeptidase and dipeptidase along the tissue and luminal contents of the hind-midgut is described. The data support a proposal concerned with how starch and protein are digested in Musca domestica larval hind-midguts and where and how midgut glycosidases and peptidases are secreted.