LOW-MOLECULAR-WEIGHT PROTEIN COMPETITION FOR BINDING-SITES ON RENAL BRUSH-BORDER MEMBRANES

Immunoglobulin light chains, beta 2-microglobulin, insulin, and lysozy me are low-molecular-weight proteins (LMWP) shown to bind to renal bru sh border membranes. Competition among these proteins and the role of electrical charge in binding to brush border membranes have not been r esolved. To investigate these factors, we performed displacement exper iments with [I-125]-labeled beta(2)-microglobulin (pI = 5.6) using six species of LMWP over a p(i) range of 4.4-11.0. The inhibition constan ts, K-i, of these six competing ligands, kappa and lambda-light chains , lysozyme, insulin, cytochrome c, and myoglobin, determined from the log displacement curves, ranged from 4x10(-5) to 9x10(-4) M. These exp eriments show marked cross-competition among LMWP for binding to brush border membranes. There was no correlation between K-i and p(i) indic ating that the molecular structure is a more important determinant of LMWP binding to brush border membranes than net electrical charge.