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 peroxiso
mes are recognized as essential components in the cellular economy of
microorganisms, plants, and mammals, little is known about their speci
alized functions in insect metabolism. Peroxisomal acyl-CoA oxidase (A
CO) is a flavin-linked, H2O2-producing enzyme that regulates the beta-
oxidation of long chain fatty acids. We measured ACO and CAT activity
in midgut tissues from worker honey bees, Apis mellifera, of known age
s from free-flying colonies. The ACO activity peaked in young worker b
ees that digest and assimilate nutrients from pollen and from trophall
axis. As the bees aged, ACO activity declined. Conversely, CAT activit
y increased as the bees aged and reached its highest level in the olde
st bees that were assayed. Isolated honey bee midguts were then fracti
onated using sucrose and Metrizamide (MET) density gradient centrifuga
tion. Organelle-bound CAT activity equilibrated in sucrose at densitie
s between 1.19 and 1.22, which are typical of spherical 1 mu m peroxis
omes. 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 microper
oxisomes. These results support our ultrastructural and cytochemical d
ata and suggest that the diverse functions of regionally specialized m
idgut epithelial cells lead to a heterogeneous population of peroxisom
al 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-ox
idants of aerobic metabolism associated with foraging and senescence.
(C) 1996 Wiley-Liss, Inc.