The role of hemolymph proline as a nitrogen sink during blood meal digestion by the mosquito Aedes aegypti

Mosquitoes utilize the amino acids derived from blood meal protein to produce egg proteins. But the amino acids can also be used to produce egg lipid or can be oxidized for energy production. These latter two processes result in the release of nitrogen as toxic ammonia. Therefore, amino acids must be processed in such a way that amino acid nitrogen can be incorporated into non-toxic waste products. Proline is the predominant amino acid in the hemolymph of the adult female mosquito Aedes aegypti. After feeding on albumin meal, hemolymph proline levels increased five-fold over unfed levels, reached maximal levels in the first hours after feeding and remained high through oviposition. Hemolymph proline levels increased as the concentration of protein in the meal increased. When starved of sugar for 24 h prior to feeding on an albumin meal, hemolymph proline levels increased four-fold over the proline levels of non-starved mosquitoes. Proline levels after feeding on a protein deficient in essential amino acids, pike parvalbumin, increased to twice the levels of albumin fed mosquitoes. Based on these observations, we propose that mosquitoes utilize proline as a temporary nitrogen sink to store ammonia arising from deamination of blood meal amino acid.