The mechanism of iodide accumulation by the brown sea weed Laminaria digitata. II. Respiration and iodide uptake.

Abstract

Iodide absorption by fresh, summer Laminaria digitata frond was accompanied by about a fivefold increase in the rate of oxygen consumption. Between approximately 3 and 6 molecules of O 2 were consumed for each iodide ion absorbed by the tissue and the respiratory quotient, whether measured in the presence or absence of iodide, lay between 0·9 and 1·1 (mean 0·94). It is argued that: (1) The iodide-stimulated respiration must occur principally near the surface of the frond, though this localization is not due to the limited diffusibility of oxygen. (2) Iodide absorption is connected with the oxidation of a carbohydrate-like compound or compounds. (3) The absorption of iodide is associated with a rate-limiting process for the oxidation of the compound or compounds. (4) Between one and two iodide ions are absorbed for each six-carbon unit oxidized. (5) Probably only one or two reactions in the oxidation of each six-carbon unit is involved in iodide absorption, one of these reactions being the rate limiting process governing the oxidation.