Methylenetetrahydrofolate Dehydrogenase and Reductase Activity in Normal and Brugia pahangi-Infected Aedes aegypti

Abstract

N',N'?-Methylenetetrahydrofolate dehydrogenase (MTHFD) and reductase (MTHFR) ac- tivity was detected in crude extracts of 4- to 5-day-old adult male and uninfected female Aedes aegypti. In such extracts, the activity of MTHFD assayed in the forward direction (forming N5,N10- methenylTHF) was approximately 25 times higher than that of MTHFR assayed in the reverse direction (forming N5,N?1-methyleneTHF). MTHFD appeared to be a dimer consisting of 2 subunits, each with a molecular weight of 105,000, had an apparent Km for N5,N10-methyleneTHF of 0.55 mM and a Km for NADP of 0.29 mM. MTHFR had a molecular weight of 220,000, had an apparent Km for N5-methylTHF of 0.2 mM and remained fully active in the absence of added FAD even after exten- sive dialysis. Suramin inhibited MTHFR activity by 50% at a concentration of 0.002 mM; MTHFD was unaffected by this drug at a concentration of 0.1 mM. The activity of MTHFD did not change in extracts of female mosquitoes prepared 7 and 12 days after they fed upon either normal or Brugia pahangi-infected jirds. The activity of MTHFR did not change in extracts of female mosquitoes pre- pared 7 days after they fed upon either normal or B. pahangi-infected jirds. The level of MTHFR was higher in older female mosquitoes. Its activity in extracts of females that were prepared 12 days after they fed upon normal jirds was approximately twice that in extracts of younger adults. Its activ- ity in extracts of age-matched females prepared 12 days after they fed upon B. pahangi-infected jirds was nearly 4 times higher than that in extracts of younger adults. It is probable that an increased amount of MTHFR was produced by the mosquito host in response to an advanced infection with B. pahangi, because MTHFR from adult B. pahangi, unlike mosquito MTHFR, was found to be FAD- dependent after 24 hr dialysis, and all assays were carried out on dialyzed mosquito extracts in the absence of FAD.