Stimulation of the sodium‐potassium pump by trypsin in low potassium type erythrocytes of goats.

1. Treatment of low K goat red cells with trypsin stimulated the Na‐K pump more than twofold. Dose dependence and time course experiments indicated a half‐maximal stimulation at 1.6 mg trypsin/ml. (37 degrees C, 3 hr), and a maximum effect after 5 hr (10 mg/ml). 2. Trypsin had only a small and variable effect on the ouabain‐insensitive component of K influx. 3. The Na‐K pump activity of high K goat red cells was not affected by trypsinization. 4. When intracellular K was varied by the PCMBS technique, it was found that the trypsin stimulation was greatest (2‐5‐fold) in cells with the highest K (40 m‐mole/1. cells) and lowest (1.1‐fold) in cells with low K (<1 m‐mole/1. cells). 5. The trypsin effect was reversed by nystatin treatment or hypotonic lysis. 6. Trypsin did not increase the number of ouabain‐binding sites. 7. It is concluded that trypsinization modifies the L antigen in low K goat red cells to decrease the apparent internal affinity for K of the Na‐K pump in these cells.