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Summary — Trypsin-like activity was detected in the epithelial tissue, in the fluid of the ectoperitrophic space, and within the endoperitrophic space of the midgut of adult worker honey bees, Apis mellifera. It was highest in free-flying bees and in caged bees fed pollen. Lower levels occurred in caged bees restricted to sucrose syrup or fed sucrose syrup in addition to either Beltsville Bee Diet or egg albumin. Levels of midgut trypsin activity were dependent on the amount of protein diet consumed. Both diet consumption and trypsin-like activity decreased as the bees aged. Ultrastructural changes in the midgut tissue accompanied this decline in enzymatic activity. In five-day-old pollen-feeding bees, the apical cytoplasm of cells in the posterior midgut contained numerous electronopaque vesicles, and the brush border in the crypts of the distal midgut was composed of short pleomorphic microvilli. Apical discharge from the midgut cells released the opaque vesicles into the midgut lumen. However, in 30-day-old field bees, the number of opaque vesicles and the microvesiculation of the brush border were reduced. Thus, the presence of the endogenously produced endoprotease and the regional variation in cell ultrastructure suggest that the honey bee may rely on countercurrent flow to distribute enzymes and nutrients efficiently throughout the midgut. Apis mellifera— midgut ultrastructure -enzymatic activity -trypsin -age

Peroxisomes are ubiquitous organelles that contain catalase (CAT) and an array of inducible enzymes that regulate aspects of lipid, purine, xenobiotic, eicosanoid, and phospholipid metabolism. Although peroxisomes are recognized as essential components in the cellular economy of microorganisms, plants, and mammals, little is known about their specialized functions in insect metabolism. Peroxisomal acyl‐CoA oxidase (ACO) is a flavin‐linked, H2O2‐producing enzyme that regulates the β‐oxidation of long chain fatty acids. We measured ACO and CAT activity in midgut tissues from worker honey bees, Apis mellifera, of known ages from free‐flying colonies. The ACO activity peaked in young worker bees that digest and assimilate nutrients from pollen and from trophallaxis. As the bees aged, ACO activity declined. Conversely, CAT activity increased as the bees aged and reached its highest level in the oldest bees that were assayed. Isolated honey bee midguts were then fractionated using sucrose and Metrizamide (MET) density gradient centrifugation. Organelle‐bound CAT activity equilibrated in sucrose at densities between 1.19 and 1.22, which are typical of spherical 1 μm peroxisomes. In the MET gradients, the organelle‐bound CAT separated into two distinct fractions. The heavier fraction equilibrated at 1.21 and the lighter fraction at 1.15, a density commonly associated with microperoxisomes. These results support our ultrastructural and cytochemical data and suggest that the diverse functions of regionally specialized midgut epithelial cells lead to a heterogeneous population of peroxisomal organelles. ACO activity confirms the role of midgut peroxisomes in the intermediary metabolism of lipids and the increasing CAT activity suggests that the midgut epithelium may metabolize deleterious pro‐oxidants of aerobic metabolism associated with foraging and senescence. © 1996 Wiley‐Liss, Inc.

Peroxisomes are ubiquitous organelles that contain catalase (CAT) and an array of inducible enzymes that regulate aspects of lipid, purine, xcnobiotic, eicosanoid, and phospholipid metabolism. Although peroxisomes are recognized as essential components in the cellular economy of microorganisms, plants, and mammals, little i s known about their specialized functions in insect metabolism. Peroxisomal acyl-CoA oxidase (ACO) is a flavin-linked, H202-producing enzyme that regulates the P-oxidation of long chain fatty acids. We measured ACO and CAT activity in midgut tissues from worker honey bees, Apis mellifera, of known ages from free-flying colonies. The ACO activity peaked in young worker bees that digest and assimilate nutrients from pollen and from trophallaxis. As the bees aged, ACO activity declined. Conversely, CAT activity increased as the bees aged and reached its highest level in the oldest bees that were assayed. Isolated honey bee midguts were then fractionated using sucrose and Metrizamide (MET) density gradient centrifugation. Organelle-bound CAT activity equilibrated in sucrose at densities between 1.19 and 1.22, which are typical of spherical 1 p m peroxisomes. In the MET gradients, the organellebound CAT separated into two distinct fractions. The heavier fraction equilibrated at 1.21 and the lighter fraction at 1.1 5, a density commonly associated with microperoxisomes. These results support our ultrastructural and cytochemical data and suggest that the diverse functions of regionally specialized midgut epithelial cells lead to a heterogeneous population of peroxisomal organelles.ACO activity confirms the role of midgut peroxisomes in the intermediary metabolism of lipids and the increasing CAT activity suggests that the midgut epithelium may metabolize deleterious pro-oxidants of aerobic metabolism associated with foraging and senescence. o 19Y6 WiIey-Liss, inc.*