Glutathione S-transferase activities in the yellow-fever mosquito [Aedes aegypti (Louisville)] during growth and aging

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Abstract
Our previous findings [Hazelton & Lang (1978) Fed. Proc. Fed. Am. Soc. Exp. Biol. 37(6), 2378 (abstr.)] demonstrated aging-specific changes in glutathione concentrations in the yellow-fever mosquito [Aedes aegypti (Louisville)]. A possible mechanism could be increased utilization via glutathione S-transferase. Thus glutathione S-transferase activities were measured in mosquito samples from the entire life span, including growth, maturity and senescence. Methods were validated for the quantitative determination of transferase activities with 1,2-dichloro-4-nitrobenzene (DCNB) and 1-chloro-3,4-dinitrobenzene (CDNB) as second substrates. Marked changes occurred during the life span, and the profiles for both DCNB and CDNB activities were identical. The activities increased throughout larval development and reached a maximum in the metamorphosis stage. The activities decreased at the end of metamorphosis in the 5-day-old adult, reached a plateau during maturity (5-20 days), and then decreased 31% (P less than 0.007) during senescence (after 33 days). This senescence-specific decrease occurred in both sexes and was localized in the abdominal region. Further kinetic analyses indicated that the lower enzyme activities were most likely due to lower amounts of active enzyme rather than a change in kinetic properties. These findings indicate that the capacity for GSH utilization via glutathione S-transferase is diminished with aging. This does not explain our previously observed decreases in GSH, but the results suggest that GSH-linked detoxification would be impaired during senescence.