The Renal Brush Border Membrane in Man. Protein Pattern, Inorganic Phosphate Binding and Transport: Comparison with Other Species

Brush border membranes (BBM) have been prepared from fresh samples of normal human kidney cortex and compared to that from mouse, rat, and rabbit. Human BBM presents a sodium dodecyl sulfate gel electrophoresis protein pattern similar to that of the animal species with 22 proteins having the same molecular weight (MW). Incubation with inorganic 32P reveals a phosphate-binding protein (MW 78,000) common to the animal species. However, the binding capacity is lower in man: 4.3 +/- 2.2 pmol Pi/mg protein compared to 9.9 +/- 2.1, 29.7 +/- 4.3, and 31.1 +/- 5.2 in rabbit, mouse, and rat, respectively. The MW of the binding protein corresponds to that of the monomer of alkaline phosphatase. Alkaline phosphatase activity follows the same increasing order in the four species. The Na gradient-dependent Pi uptake by human BBM vesicles is low: Vmax is 0.90 +/- 0.05 nmol/mg/20 s compared to 1.3 +/- 0.1, 1.5 +/- 0.2, and 5.2 +/- 0.2 in rabbit, mouse, and rat, respectively. However, the Km values are within the same range for the four species.