text: Increased Cat3-mediated cationic amino acid transport functionally compensates in Cat1 knockout cell lines.
  Arginine transport is important for a number of biological processes in vertebrates, and its transport may be rate-limiting for the production of nitric oxide. The majority of L-Arg transport is mediated by System y+, although several other carriers have been kinetically defined. System y+ cationic amino acid transport is mediated by proteins encoded by a family of genes, Cat1, Cat2, and Cat3. High affinity L-arginine transport was investigated in embryonic fibroblast cells derived from Cat1 knockout mice that lack functional Cat1. Both wild type and knockout cells transport arginine with comparable Km and Vmax. However, the apparent affinity for lysine transport was 2.4 times lower in Cat1(-/-) cells when compared with wild type cells, a property characteristic of Cat3-mediated transport. Northern analysis-documented Cat2 mRNA increased 2-fold, whereas Cat3 mRNA levels increased 11-fold in Cat1(-/-) relative to Cat1(+/+) cells. The low affinity Cat2a mRNA was not detectably expressed in these cells. Even though Cat3 expression is normally limited to adult brain, there was a large increase in the amount of Cat3 protein present at the plasma membrane of Cat1(-/-) embryonic fibroblast cells. These results suggest that Cat3 compensates for the loss of functional Cat1 in cells derived from Cat1 knockout mice and mediates the majority of high affinity arginine transport.
entities.id: T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T1 T20 T21 T22 T23 T24 T25 T26 T27 T28 T29 T2 T30 T31 T3 T4 T5 T6 T7 T8 T9
entities.type: GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-N GENE-N GENE-Y GENE-Y CHEMICAL GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-N CHEMICAL GENE-Y GENE-Y CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL
entities.text: Cat3 Cat3 Cat1 Cat3 Cat1 Cat1 System y+ System y+ Cat1 Cat2 Arginine Cat3 Cat1 Cat1 Cat1 Cat3 Cat2 Cat3 Cat1 Cat1 Cat2a arginine Cat3 Cat1 nitric oxide L-Arg amino acid L-arginine arginine lysine amino acid