Effect of low-molecular-weight proteins on protein (lysozyme) binding to isolated brush-border membranes of rat kidney.
Filtered proteins including the low-molecular-weight protein lysozyme are reabsorbed by the proximal tubule via adsorptive endocytosis. This process starts with binding of the protein to the brush-border membrane. The binding of 125I-labelled egg-white lysozyme (EC 3.2.1.17) to isolated brush-border membranes of rat kidney and the effect of several low-molecular weight proteins on that binding was determined. The Scatchard plot revealed a one-component binding type with a dissociation constant of 5.3 microM and 53.0 nmol/mg membrane protein for the number of binding sites. The binding of the cationic lysozyme was inhibited competitively by the addition of cationic cytochrome c to the incubation medium, while the neutral myoglobin had no effect. The anionic beta-lactoglobulin A inhibited the lysozyme binding in a noncompetitive manner. These data suggest that the binding takes place between positively charged groups of the protein molecule and negative sites on the brush-border membrane, and, the competition between the cationic cytochrome c and the cationic lysozyme for the binding sites may be responsible for the inhibitory effect of cytochrome c on renal lysozyme reabsorption. The binding step at the brush-border membrane appears to be cation-selective.
D000818:Animals; D001667:Binding, Competitive; D003574:Cytochrome c Group / Q000378:metabolism; D007672:Kidney Cortex / Q000648:ultrastructure*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008871:Microvilli / Q000201:enzymology; D009113:Muramidase / Q000378:metabolism*; D051381:Rats
D003574:Cytochrome c Group; D008565:Membrane Proteins; D009113:Muramidase