title: Metabolism of amino acids during hyposmotic adaptation in the whiteleg shrimp, Litopenaeus vannamei.
abstract: The penaeid prawn, Litopenaeus vannamei, was employed to investigate intracellular isosmotic regulation in situations where invertebrates encounter hyposmosis. Hemolymph osmolality was first analyzed to confirm osmoregulatory conditions in the experimental animals, followed by analysis of amino acids in muscle and hemolymph using high-performance liquid chromatography. Total muscle amino acid levels decreased when hemolymph osmolality was extremely low, whereas glycine and L-serine levels increased in the hemolymph. These results suggest that tissue amino acids were released into the hemolymph to lower the osmolality of the tissues for purposes of low-salinity adaptation. Next, oxygen consumption and ammonia excretion rates were examined, and the O/N ratio was determined. Oxygen consumption levels and ammonia excretion rates increased, and the O/N ratio decreased when the animals were exposed to low salinity. These results suggest that amino acids were abundantly consumed as an energy source when animals were exposed to low salinity. To confirm the consumption of particular amino acids, the specific activity of L-serine ammonia lyase was also examined. Specific activity was highest when L-serine levels in the hemolymph were highest. Thus, it appears that L-serine levels increased under hyposmotic conditions due to the consumption of L-serine as an energy source. It was concluded that particular amino acids as osmolytes are likely metabolized as energy sources and consumed for purposes of hyposmotic adaptation.
authors.affiliation: Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
authors.forename: Junpei
authors.initials: J
authors.lastname: Shinji
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Okutsu
authors.forename: Vidya
authors.initials: V
authors.lastname: Jayasankar
authors.forename: Safiah
authors.initials: S
authors.lastname: Jasmani
authors.forename: Marcy N
authors.initials: MN
authors.lastname: Wilder
mesh_terms: D000222:Adaptation, Physiological; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005998:Glycine / Q000378:metabolism; D006458:Hemolymph / Q000378:metabolism*; D012695:L-Serine Dehydratase / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000378:metabolism*; D009994:Osmolar Concentration; D010101:Oxygen Consumption / Q000502:physiology; D033561:Penaeidae / Q000502:physiology*; D054712:Salinity; D012694:Serine / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D012694:Serine; D000641:Ammonia; D012695:L-Serine Dehydratase; D005998:Glycine