Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954 electrolytesinbi00shan Year: 1955 GEORGE T. SCOTT AND HUGH R. HAYWOOD 45 A logical explanation of the action of iodoacetate in the dark is that the glycolytic breakdown of carboliydrate is blocked at the level of phosphoglycer- aldehyde dehydrogenase, the principal site of attack of this inhibitor (14). Accordingly, metabolic energy apparently required for cation regulation is no longer supplied; potassium is lost and sodium
Electrolytes in biological systems, incorporating papers presented at a symposium at the Marine Biological Laboratory in Woods Hole, Massachusetts, on September 8, 1954 electrolytesinbi00shan Year: 1955 GEORGE T. SCOTT AND HUGH R. HAYWOOD 45 A logical explanation of the action of iodoacetate in the dark is that the glycolytic breakdown of carboliydrate is blocked at the level of phosphoglycer- aldehyde dehydrogenase, the principal site of attack of this inhibitor (14). Accordingly, metabolic energy apparently required for cation regulation is no longer supplied; potassium is lost and sodium gained by the cell. The prevention of these ions shifts by light further supports this hypothesis, since phosphoglyceric acid, the compound which is formed by the action of phos{)hoglyceraldehyde dehydrogenase, has been shown to be the first stable product formed in the photosynthetic reduction of carbon dioxide (3, 13). 4 00 Fig. 5. Influence of m/1. iodoacetate on the potassium and sodium content of Valonia macrophysa in the light and dark. Hence, in the light, even in the presence of the inhibitor, which prevents the glycolytic formation of phosphoglyceric acid, this intermediate is made avail- able to cellular metabolism by photosynthesis. The postulated reactions are summarized in figure 21. In the interpretation of the prevention by light of the iodoacetate effect it is essential to know whether or not the cell when illuminated is permeable to the inhibitor. In order to examine this problem the inhibitor was added to samples of Ulva in the light and maintained for 12 hours. At this time samples were transferred to sea water without the inhibitor and placed in the dark. Typical results are presented in figures 6 and 7, indicating a marked loss of potassium and gain of sodium after transfer to the inhibitor-free medium in the dark. Washing-out of the iodoacetate elBfect. It is of interest to determine whether or not the ion shifts caused by iodoacetate in the dark a
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