CATALYTIC EFFECTS OF CARBON DIOXIDE IN CARBON DIOXIDE ASSIMILATING CELLS

It has been confirmed that absence of carbon dioxide may decreasethe rate of oxygen production which accompanies the photochemicalreduction of p-benzoquinone in algae and chloroplasts. Thisinfluence of carbon dioxide partial pressure does not applyto the overall oxygen yield. In the blue-green alga Anacystisnidulans the initially small carbon dioxide deficiency effectincreases with time spent in the dark. The deterioration ofreaction rates is counteracted by light. There seems to be nodirect connection or interdependence between the photosyntheticreduction of carbon dioxide and the sensitivity of some partof the photochemical mechanism to loss of carbon dioxide. Notonly does addition of quinone to living cells in these experimentsdestroy their capacity for photosynthesis, but mutant cellsthat never had this capacity still retain the sensitivity towardslack of carbon dioxide when tested for their ability to reducequinone. Many different metabolic reactions have been seen topossess such dependency on traces of carbon dioxide, also innon-photosynthetic cells and tissues. The explanation for "catalytic"effects of carbon dioxide ought to be a general one–suchas an influence on the efficiency of certain phosphorylationswhich occur everywhere in the living world. ¹ Dedicated to Prof. H. TAMIYA on the occasion of his 60th birthday.These studies were aided by contract NONR 988 (10) between theOffice of Naval Research, Department of the Navy, and the FloridaState University, respectively. ² Present address: Charles F. KETTERING Research Laboratories,Yellow Springs, Ohio. (Received December 7, 1962; )     

THE DIFFUSION OF CARBON DIOXIDE IN TISSUES

1. Two methods are given for measuring the rate of diffusion of CO₂ in tissue membranes. Methods are also given for the determination of tissue thickness and the absorption coefficient for CO₂ in tissues. 2. The values obtained for the permeability constant (P x 10⁴) at 22°C. for CO₂ in the following tissues are:—frog skin, 3.05; connective tissue (dog), 2.65; smooth muscle (cat), 5.00; frog muscle, 5.29; striated muscle (dog), 4.70. P is expressed as cc. per cm.² per minute under a pressure gradient of one atmosphere per cm. 3. Evidence is presented to show that in a "steady state" bicarbonate contributes a negligible amount to the diffusion of CO₂. 4. The absorption coefficient for CO₂ in frog skin is 0.73 cc. per cc. and for frog muscle 0.78 cc. per cc. 5. In all of the tissues studied the diffusion of CO₂ is slower than in water. The diffusion coefficients (K x 10⁴ in cm.²/minute) at 22°C. for tissues as compared with water are:—water (16°C.), 9.5 (Hüfner, 1897); frog skin, 4.1; connective tissue, 3.7; frog muscle, 6.8; striated muscle (dog), 6.0; smooth muscle (cat), 6.4. 6. The time course of saturation of a tissue with CO₂ is altered in the presence of available base. Non-acidified tissues saturate more slowly than acidified tissues and the rate of saturation is dependent on the CO₂ tension.     

THE PRODUCTION OF CARBON DIOXIDE BY NERVE

1. A modified Osterhout respiratory apparatus for the detection of CO₂ from nerve is described. 2. The lateral-line nerve from the dogfish discharges CO₂ at first with a gush for half an hour or so and then steadily at a lower rate for several hours. 3. Simple handling of the nerve does not increase the output of CO₂; cutting it revives gush. 4. The CO₂ produced by nerve is not escaping simply from a reservoir but is a true nervous metabolite. 5. The rate of discharge of CO₂ from a quiescent nerve varied from 0.0071 to 0.0128 mg. per gram of nerve per minute and averaged 0.0095 mg. 6. Stimulated nerve showed an increased rate of CO₂ production of 15.8 percent over that of quiescent nerve. 7. The results of these studies indicate that chemical change is a factor in nerve transmission.     

THE EXCRETION OF CARBON DIOXIDE BY FROG NERVE

1. Quiescent sciatic nerve of the frog discharges CO₂ at the average rate of 0.00876 mg. CO₂ per gram of nerve per minute. 2. Sciatic nerve steeped one minute in boiling water discharges CO₂ at first at a low rate and after an hour and a half not at all. 3. Degenerated sciatic nerve discharges CO₂ at a slightly higher rate than normal living nerve does. 4. Connective tissue from the frog discharges CO₂ at an average rate of 0.0097 mg. per gram of tissue per minute. 5. Assuming that a nerve is composed of from one-half to one-quarter connective tissue the CO₂ output from its strictly nervous components is estimated to be at a rate of 0.008 mg. CO₂ per gram of nerve per minute. 6. Stimulated sciatic nerve increases the rate of its CO₂ output over quiescent nerve by about 14 per cent. When this number is corrected for strictly nervous tissue the rate is about 16 per cent. 7. The increased rate of CO₂ production noted on stimulation in normal sciatic nerves was not observed when they were boiled, blocked, or degenerated. It was also not observed with stimulated strands of connective tissue.     

CARBON DIOXIDE PRODUCTION AND DURATION OF LIFE OF DROSOPHILA CULTURES

The total CO₂ produced by aseptic Drosophila cultures during the entire duration of life has been determined at 15°, 26°, and 30°C. in the dark and at 22–26°C. in the light. The total amount of CO₂ produced is not constant but is greater at 15° than at 26° or 30°, and is much greater in the light than in the dark. The total duration of life, therefore, is not determined by the time required to produce a limiting amount of CO₂.     

THE INFLUENCE OF LIGHT AND CARBON DIOXIDE ON PHOTOSYNTHESIS

1. An optical system is described which furnishes an intensity of 282,000 meter candles at the bottom of a Warburg manometric vessel. With such a high intensity available it was possible to measure the rate of photosynthesis of single fronds of Cabomba caroliniana over a large range of intensities and CO₂ concentrations. 2. The data obtained are described with high precision by the equation KI = p/(p ² _max. – p ²)^½ where p is the rate of photosynthesis at light intensity I, K is a constant which locates the curve on the I axis, and p _max. is the asymptotic maximum rate of photosynthesis. With CO₂ concentration substituted for I, this equation describes the data of photosynthesis for Cabomba, as a function of CO₂ concentration. 3. The above equation also describes the data obtained by other investigators for photosynthesis as a function of intensity, and of CO₂ concentration where external diffusion rate is not the limiting factor. This shows that for different species of green plants there is a fundamental similarity in kinetic properties and therefore probably in chemical mechanism. 4. A derivation of the above equation can be made in terms of half-order photochemical and Blackman reactions, with intensity and CO₂ concentration entering as the first power, or if both sides of the equation are squared, the photochemical and Blackman reactions are first order and intensity and CO₂ enter as the square. The presence of fractional exponents or intensity as the square suggests a complex reaction mechanism involving more than one photochemical reaction. This is consistent with the requirement of 4 quanta for the reduction of a CO₂ molecule.