Physiology of protein digestion in the midgut of the honeybee (Apis mellifera L.)

Proteolytic activity in the midguts of pupae and imagos of worker honeybees was determined over a 1-yr period. The bees were of defined ages and the size of the hypopharyngeal glands was used as a parameter of their functional status. The activities of trypsin-like, chymotrypsin-like enzymes and the total caseinolytic activity were investigated; they did not depend on Ca²⁺ and showed optimal turnover at pH values above 7. Proteolytic activity is limited in pupae and newly emerged bees, then increases rapidly in the first hours of the imago stage. Proteolytic activity and the relation between trypsin- and chymotrypsin-like activity vary with age, season and functional status of the insects. Nurse bees show the greatest proteolytic activity. Age-dependent distributions of enzymatic activities in the endo- and ecto-peritrophic space indicate that the peritrophic membrane establishes compartments within the midgut lumen.