Transport of Tricarboxylic Acid Cycle Intermediates by Membrane Vesicles from Renal Brush Border

• Published in: Proceedings of the National Academy of Sciences - PNAS 1979-07, Vol.76 (7), p.3397-3400
• Main Authors: Kippen, Ian, Hirayama, Bruce, Klinenberg, James R., Wright, Ernest M.
• Format: Article
• Language: English
• Subjects: Amino acid metabolism; Amino acids; Amino sugars; Animals; Binding, Competitive; Biological Transport, Active; Cellular metabolism; Citrates; Citrates - metabolism; Citric Acid Cycle; In Vitro Techniques; Ketoglutaric Acids - metabolism; Kidney Tubules, Proximal - metabolism; Kinetics; Microvilli; Microvilli - metabolism; P branes; Rabbits; Sodium; Sugar acids; Tricarboxylic acid cycle
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.76.7.3397

The uptake of citrate and α -ketoglutarate by membrane vesicles from rabbit renal brush border was studied by a rapid filtration technique. Both compounds exhibited transport characteristics similar to those seen for the sodium-dependent cotransport systems previously described for sugars and amino acids in brush border membranes. The estimated sodium-dependent Vmaxand Kmwere 17 nmol per mg of protein per min and 0.18 mM for citrate and 17 nmol per mg of protein per min and 1.0 mM for α -ketoglutarate. The initial rate of citrate transport was 5 times that of sugars and amino acids under comparable conditions. Uptake rates of 0.1 mM citrate and α -ketoglutarate were inhibited by >90% by 10 mM succinate, malate, fumarate, or oxaloacetate, indicating the presence in the brush border membrane of a transport system highly specialized for the renal conservation of intermediates of the tricarboxylic acid cycle.