title: The binding of beta-2-microglobulin to renal brush-border membrane: affinity measurement, inhibition by serum albumin.
abstract: In the kidney, filtered proteins are rapidly reabsorbed so that the final excretion is less than 0.1% of the filtered amount for low molecular weight proteins such as beta 2-microglobulin and a few percent for albumin. In order to investigate the affinity of proteins for luminal membranes, rat renal brush-border membranes were incubated with 125I-labelled human beta 2-microglobulin and the initial binding rate determined by the filtration method. Scatchard plot analysis of binding rate revealed two types of binding sites: one with Km = 0.25.10(-6) M and Vmax = 0.1 nmol/min per mg protein and another with Km = 1.10(-5) M and Vmax = 1.3 nmol/min per mg protein. The lower affinity type is likely to represent non-specific binding the physiological role of which is to be discussed. The higher affinity sites seem to play the major role in binding rate. beta 2-Microglobulin initial binding is reversible, and inhibited by bovine serum albumin. Comparison of the time course of bound beta 2-microglobulin removal by unlabelled beta 2-microglobulin and by albumin suggests that these two proteins have a different internalization mechanism.
mesh_terms: D000510:Alpha-Globulins / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D007328:Insulin / Q000494:pharmacology; D007457:Iodine Radioisotopes; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008871:Microvilli / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012709:Serum Albumin / Q000494:pharmacology*; D001613:beta 2-Microglobulin / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000510:Alpha-Globulins; D007328:Insulin; D007457:Iodine Radioisotopes; D012709:Serum Albumin; C025500:alpha(2)-microglobulin; D001613:beta 2-Microglobulin