PubMed · 8855161
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J F Livesey, J G Donnelly, D S Ooi. 1996. HPLC screening method for cystinuria.. https://pubmed.ncbi.nlm.nih.gov/8855161/
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The transport mechanism of the reconstituted ornithine/citrulline carrier purified from rat liver mitochondria was investigated kinetically. A complete set of half-saturation constants (K(m)) was established for ornithine, citrulline and H(+) on both the external and internal side of the liposomal membrane. The internal affinity for ornithine was much lower than that determined on the external surface. The exclusive presence of a single transport affinity for ornithine on each side of the membrane indicated a unidirectional insertion of the ornithine/citrulline carrier into liposomes, probably right-side-out with respect to mitochondria. Two-reactant initial velocity studies of the homologous (ornithine/ornithine) and heterologous (ornithine/citrulline) exchange reactions resulted in a kinetic pattern which is characteristic of a simultaneous antiport mechanism. This type of mechanism implies that the carrier forms a ternary complex with the substrates before the transport reaction occurs. A quantitative analysis of substrate interaction revealed that rapid-equilibrium random conditions were fulfilled, characterized by a fast and independent binding of internal and external substrates.
Decreased availability of arginine and impaired production of NO (nitric oxide) have been implicated in the development of endothelial dysfunction. Citrulline formed by the NOS reaction is recycled to arginine by the citrulline-NO cycle, which is composed of NOS, argininosuccinate synthetase (AS), and argininosuccinate lyase. Therefore, we investigated the alterations of these enzymes in the aorta of streptozotocin (STZ)-induced diabetic rats. eNOS and AS mRNAs were increased by three- to fourfold 1-2 weeks after STZ treatment and decreased at 4 weeks. AL mRNA was weakly induced. Induction of eNOS and AS proteins was also observed. Cationic amino acid transporter (CAT)-1 mRNA remained little changed, and CAT-2 mRNA was not detected. The plasma nitrogen oxide levels were increased 1-2 weeks after STZ treatment and decreased at 4 weeks. Transforming growth factor-beta1 (TGF-beta1) mRNA in the aorta was also induced. TGF-beta1 induced eNOS and AS mRNAs in human umbilical vein endothelial cells but inhibited the proliferation of HUVEC. These results indicate that eNOS and AS are coinduced in the aorta in early stages of STZ-induced diabetic rats and that the induction is mediated by TGF-beta1. The results also suggest that TGF-beta1 works antiatherogenically at early stages of diabetes by increasing NO production, whereas prolonged elevation of TGF-beta1 functions atherogenically by inhibiting endothelial cell growth.
A fusion protein (F-SU/GFP) which is comprised of the surface (SU) subunit of the Friend MuLV envelope glycoprotein and the green fluorescence protein (GFP) was generated by a baculovirus expression system. The F-SU/GFP specifically bound to mammalian tissue cultured cells expressing the mCAT-1, the receptor for ecotropic murine leukemia virus (ECO-MuLV). The expression level of mCAT-1 on hematopoietic cells was measured based on the capacity of cells to absorb the F-SU/GFP. In BALB/c mice susceptible to Eco-MuLV infection, all hematopoietic cell subpopulations absorbed the F-SU/GFP with the most prominent absorption observed in the TER119+ erythroblasts. Hematopoietic cells from C4W and AKR mice did not absorb the F-SU/GFP as readily as the BALB/c cells, probably due to expression of the envelope glycoproteins of endogenous Eco-MuLVs in these mice. Although AKR mice are susceptible to Eco-MuLV infection while C4W mice are resistant, these mice showed no apparent difference in the F-SU/GFP-absorbing capacity.