The influence of certain agents on the activity of phospho-nuclease

The influence of certain chemical agents on the action of the phospho-nuclease of the intestinal mucosa of the hog was studied. In most cases 2 per cent. solutions of the substances tested were used with 10 c.c. of a 20 per cent. tissue extract, and 5 c.c. of 2 per cent. solution of neutral sodium nucleate.

Salts of Ca, Ba, Sr, and Li inhibited the action considerably while Mg, the phosphate of which is more soluble, did not inhibit. Uranium salts entirely inhibited. The inhibition in these cases appears to be due mainly to the removal of phosphate. The salts of the heavy metals, Hg, Ag, Cu, and U almost entirely inhibited while lead salts had less effect. The effect of these latter may be largely due to destruction of the enzyme.

Oxalate, tartrate, and fluoride had marked inhibitory effect while citrate did not show this. With the exception of citrate these form insoluble salts with Ca. Apparently the inhibitory action is due to removal of Ca ions. The suggestion that a slightly acid solution was favorable could not be confirmed. HCI to make 0.05 per cent. solution practically stopped the action while an equal amount of NaOH doubled the amount of phosphoric acid set free. The same favorable effect was found when a little NaHCO₃ was added and the mixture saturated with CO_2. Apparently a slightly alkaline or balancing solution is favorable. NaCl, K₂SO₄ and KI stimulated slightly. NH₄NO₃ and potassium arsenite inhibit somewhat. KCN in .25 per cent. neutral solution paralyzed the action. In all of these cases the protective action of the protein of the intestinal extract must be borne in mind.

The inhibition by Ca precipitants may aid in explaining the toxicity of these agents for nucleated cells.