title: Discrimination of transport systems of L-tyrosine in mouse mammary gland: characterization of system T.
abstract: On the basis of inhibition analysis, tyrosine uptake in mouse mammary gland was found to be mediated by Na(+)-dependent and Na(+)-independent systems. Na(+)-dependent system was insensitive to 2-(methylamino) isobutyric acid (MeAIB), with an apparent Km of 1.67 mM and maximal velocity 74.5 nmol.g-1 cell. min-1. Competition experiments showed the presence of two distinct Na(+)-independent components of tyrosine uptake. One component was sensitive to 2-aminobicyclo (2,2,1) heptane-2-carboxylic acid (BCH) and was similar to the system L, with an apparent Km of 0.23 mM and maximum velocity of 31 nmol.g-1 cell.min-1. Second component was BCH-insensitive but tryptophan-sensitive, with an apparent Km of 15.75 mM and Vmax of 157.5 nmol.g-1cell.min-1. BCH-insensitive, tryptophan-sensitive system was a low affinity system. It approached steady state slowly and was more sensitive, relative to the system L, to n-ethylmaleimide inhibition. Tyrosine uptake through this system did not respond to trans-stimulation, whereas system L mediated uptake responded considerably. BCH-insensitive, tryptophan-sensitive component of Na(+)-independent tyrosine uptake is attributed to the system T, previously described only in human red blood cells and rat liver cells.
authors.affiliation: Animal Biochemistry Division, National Dairy Research Institute, Kamal, India.
authors.lastname: Rekha
authors.forename: V K
authors.initials: VK
authors.lastname: Kansal
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D005260:Female; D008321:Mammary Glands, Animal / Q000378:metabolism*; D051379:Mice; D012964:Sodium / Q000502:physiology*; D013237:Stereoisomerism; D014443:Tyrosine / Q000493:pharmacokinetics*
chemical_list: D014443:Tyrosine; D012964:Sodium