Intracellular distribution of hexokinase in the tissue zones of rat kidney.

The high rates of aerobic glycolysis of tumor cells and brain may result from an increased binding of hexokinase (ATP: D-hexose 6-phosphotransferase, EC 2.7.1.1) to mitochondria. Renal papillary tissue also has a high rate of aerobic glycolysis. Therefore, the activity of hexokinase, in the mitochondrial and cytoplasmic fractions of the cortical, medullary and papillary regions of rat kidney were determined. There was an increasing cortico-papillary gradient for the specific activity (mol/kg protein per h) of total hexokinase. The specific activity of the cell-free whole homogenates of cortex, medulla and papilla were (n = 8): 0.85 +/- 0.04; 2.09 +/- 0.08; 3.76 +/- 0.15, respectively. The specific activity of hexokinase in the papillary mitochondrial fraction (5.91 +/- 0.40) was significantly greater (P less than 0.005) than in the papillary cytoplasmic fraction, (3.40 +/- 0.13). The selectivity higher specific activity for hexokinase in the papillary mitochondrial fraction was in sharp contrast with the specific activity of critical (0.96 +/- 0.07) or medullary (2.28 +/- 0.16) mitochondrial fractions, which have hexokinase specific activities which were not significantly different from those present in their respective cytoplasmic fractions. These observations suggest that the high rate of aerobic glycolysis of renal papillary tissue may be due, at least in part, to the high specific activity of hexokinase associated with the papillary mitochondrial fraction.