On the Physiology of Amoeboid Movement

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Abstract
A The action of isotonic sucrose, glucose, glycerol and urea on a marine amoeba has been studied. Experiments were performed with these to elucidate the action of calcium on locomotion. No movement occurs in these pure nonelectrolytes. The amoebae have remarkable powers of survival in pure isotonic nonelectrolytes (1·05 M). Survival ranges from 1 hour in the sugars to over 16 hours in the urea. Survival in the latter is far longer than in any other pure solution, including salts. Even when the concentration is as low as 0·04 M, the sugars tested inhibit movement in solutions which normally support it. Addition of calcium to glycerol does not support movement. But an optimum mixture of NaCl + CaCl2 which supports movement will suffer at least 75 per cent, dilution with isotonic glycerol and yet maintain movement. The addition of calcium to urea allows good movement over a wide range of low calcium concentrations: movement at the optimum is maintained for over 12 hours. The addition of urea to optimal mixtures of NaCl + CaCl2 necessitates the further addition of calcium to balance the effect of the added urea. The rôle of calcium in the external medium in relation to movement is reviewed. The physiological action of urea in these amoebae is compared with its action on many cells. It is suggested that the long survival and continued movement in the presence of urea is related to the maintenance of a condition of impermeability to dissolved substances at the cell surface. It is pointed out that this is in agreement with the denaturing action of urea in strong solutions on proteins. The possible significance of this in the adaptation of cell surfaces to a freshwater environment is mentioned. B An attempt has been made to determine the iso-electric point of the proteins of a marine amoeba by staining with methylene blue and eosine after fixation in alcohol. There appears to be a fairly definite iso-electric point between pH 4·6 and 5·0. This is at a considerable distance on the acid side from the pH at which movement is inhibited in the amoebae. It is suggested that sol ⇌ gel changes accompanying amoeboid movement cannot be related simply to the external H-ion concentration in a manner comparable to the relation of the latter to the properties of simple protein systems around the iso-electric point.