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Studies of excitable membrane formed on the surface of protoplasmic droplets isolated from Nitella. V. Effect of the chemical modification of membrane proteins with SH reagents of excitability

1974; Elsevier BV; Volume: 367; Issue: 1 Linguagem: Inglês

10.1016/0005-2736(74)90131-x

1879-2642

Isao Inoue, N Ishida, Yonosuke Kobatake,

Cephalopods and Marine Biology

Two SH reagents, p-chloromercuribenzoate and N-ethylmaleimide, and one reducing agent, dithiothreitol, were applied extrinsically to the surface membrane of protoplasmic droplets isolated from Nitella. The electrophysiological properties of the membrane and the tension at the surface of the droplets were examined in conjunction with the chamical modifications. The results obtained are summarized as follows: 1. The excitability of the drop membrane was suppressed irreversibly when the drop was treated either with 0.2 mM p-chloromercuribenzoate or 1 mM N-ethylmaleimide. All droplets treated with SH reagents were disrupted within an hour when the period of the treatments exceeded 5 min. During the process of disruption, the membrane potential and the electric resistance increased. The surface tension decreased temporarily by a factor of 10−3 (from 10−1 to 10−4 dyne/cm) then increased and approached 10u−1 dyne/cm in the p-chloromercuribenzoate solution without recovery of the excitability. 2. Application of 4 mM dithiothreitol against the p-chloromercuribenzoate-treated droplet led to a gradual but complete restoration of the membrane potential, electric resistance and excitability. 3. The excitability which was suppressed by the treatment with SH reagents could also be recovered by means of alternative exchanges of the external media with dilute and concentrated salt solutions. These results imply that the processes of depolarization and repolarization caused by the external media are accompanied by a considerable variation in the composition of molecules constituting the surface membrane of the protoplasmic droplets.