SUMMARY: The unidirectional K fluxes across the mycelial surface of were determined using K. Influx was mediated by at least two kinetically distinct systems, one having an apparent of 6·5 μ-equiv. K+/1 and the other of about 1·0 m-equiv. K/1. The V for both systems was in the range 18 to 22 μ-equiv. K/100 mg mycelial dry matter/h (1·0 to 1·2 m-equiv. K/1 cell-water/min). Influx was strongly inhibited by 2,4-dinitrophenol, sodium azide, sodium arsenate and anaerobiosis. K efflux was dependent on the external K concentration and ranged from 3 to 10% of mycelial K/h. The maximum efflux rate was always considerably less than the initial influx rate for the K concentrations examined. During incubation in dilute KC1 solutions, K influx decreased to a value approaching the K efflux rate. It is considered that equilibrium with external K is attained primarily by the regulation of K influx, and that this may be the principal mechanism controlling cytoplasmic K+ levels.

Adsorption of K was also observed throughout the K concentration range examined and can be attributed to two distinct K-binding entities at the mycelial surface, half-saturating at approximately 0·1 mM- and 4·4 mM-KCl respectively.


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