Abstract
1. Phosphatase Experiments. Several authors 1 , 2 , 3 have reported that phlorizin does not appreciably affect the phosphatase activity of kidney extracts. In all cases their findings are apparently concerned with the alkaline phosphatase, since the determinations were made within the pH range of 7.6 to 9.2. It was thought of interest to determine the effects of phlorizin on the acid phosphatase activities of kidney cortex and intestinal mucosa extracts.
The filtered extracts were prepared as described by Kay, 4 brought to pH 5.2 by addition of 1 part in 7 of veronal-acetate buffer, to preserve the acid phosphatase, and kept on ice until used. Determinations of phosphatase activity were carried out at 37°C as described by Belfanti and coworkers. 5 The results are shown in Fig. 1.
At pH about 5 the rate at which inorganic phosphate is formed from glycerophosphate in the presence of kidney cortex extracts is markedly decreased by m/100 phlorizin, and in some instances is appreciably decreased by m/300 and even m/1000 phlorizin. With increase in pH the inhibition becomes less, until at and beyond pH 7 (up to pH 9) even m/100 phlorizin has practically no inhibitory action on the phosphatase activity.
When intestinal mucosa extracts were employed marked inhibition was secured only in Exp. 3, in which hexosediphosphate was employed as substrate. In 2 other experiments, using glycerophosphate as substrate, the results at pH below 7 were irregular, and at pH about 7 phlorizin actually produced an acceleration of the rate of disappearance of inorganic phosphate. In the alkaline pH range (7 to 9) the values for control tubes and for phlorizin-containing tubes were practically identical.
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