mentation behavior in aligned tubes of cylindrical shape and came u p with a cell having these characteristics: • Sedimentation isn't complicated by a barrier and adequate volumes can be handled. • Isolation of portions of t h e solution is positive, reproducible, a n d does not depend upon density gradients. • AU dimensions and volumes are accurately known a n d are reproducible.
The result, says Ray, is a multiple sheared boundary cell and rotor. Cell spaces in the apparatus are merely holes in five disks stacked together. Alternate disks, keyed to a shaft, are rotated 90 degrees, w h i c h isolates five fractions of the solution. Ray says the cell enabled him to learn that no density gradient is necessary to stabilize sedimentation of extremely dilute polystyrene latex.
Probing the Photosynthesis Cycle Maintenance requirements for CO2 reduction cycle determined; respiration may be energy source F A C H OF THE STEPS in the
photosyn-
*-* thetic carbon dioxide reduction cycle has been determined, and it is now possible to define reagent requirements to maintain it. T h e requirement for reduction of one molecule of carbon dioxide is four equivalents of. hydrogen a n d three molecules of adenosine triphosphate ( A T P ) . Photochemical reactions must b e t h e suppliers of these. This specific ratio of hydrogen to ATP suggests t h e possibility that respiration might contribute some of the energy required for photosynthesis by supplying some of t h e ATP. Using a cell-free system, Melvin Calvin of the University of California performed the last and unique reaction occurring in the cycle. Calvin discussed his work before t h e Organic Symposium held recently at Purdue. Ribulose diphosphate is used as a substrate. Purification of t h e carboxydismutase enzyme system confirms t h e existing deduction that carboxylation of t h e ribulose compound leads directly to t w o molecules of phosphoglyceric acid (PGA). Reduction of PGA with the help of ATP gives rise to a triose phosphate, which reacts in the cycle to give hexoses. The eventual formation of sucrose is followed b y a "sugar rearrangement" into five- a n d sevencarbon molecules, ultimately completing the reduction cycle b y reforming t h e starting ribulose diphosphate. Carboxylation again takes place, being the initiating mechanism for the series. Respiration M a y Be Energy Source. Respiration as a possible energy source was studied by the California group by measuring the requirement of photosynthesis at various ratios of photosynthetic rate to respiration rate. Experiments determining quantum requirements show an uncorrected value of 7.4 for the upper limit as the photosynthetic rate increases, a n d a corrected value of 4 as the rate approaches zero and ordinary respiratory rates can keep up. VOLUME
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The apparent limiting values of these quantum requirements indicates an additional source of ATP. Current knowledge of t h e photochemical reaction, or those closely related, is limited to t h e breakdown of water into active oxygen—some of which is evolved as molecular oxygen—and hydrogen—some of which is recombined with the active oxygen to form water. The remainder of t h e hydrogen is utilized in the cycle. T h e relationship b e t w e e n quantum capture, oxygen evolution, and the photosynthetic cycle is t h e triggering action for photosynthesis. Thioctic Acid Role. Working to determine the relation of thioctic acid to the photochemical act, the group studied the effect of light intensity on the appearance of radiocarbon in the tricarboxylic acid cycle of photosynthesis. This work implicates the sulfurbearing acid. Calvin suggests that absorption of light creates conduction electrons (reducing agent) within a chlorophyll containing layer. These electrons are separated from the remaining "holes" (oxidizing agent) because of the structure of t h e lamina in the subchloroplast structural units. Donation of electrons from water molecules, or closely related material, traps the holes. Simultaneously, the electrons are accepted by the sulfur atoms of thioctic acid to produce a ditliiol. Hydrogen from t h e mercaptan is in turn passed on to other carriers, and ultimately to phosphoglyceric acid. • Ester and o t h e r difficultly reducible groups can b e reduced rapidly at room temperature with sodium borohydride in the presence of aluminum chloride. Herbert C. Brown and B. C . Subba Rao of Purdue find that nitro and amide groups are not reduced, so the method offers a convenient procedure for selective reduction of nitro esters. Their work suggests that t h e reducing prop-
JULY
4,
1955
Research Progress a t Brookhaven The cosmotron and nuclear reactor supported a large fraction of the research effort at Brookhaven National L a b in the year ending July 1, 1954. According to the annual report, "each machine turned i n an exceptionally fine performance record." Among the advances noted on the chemistry front: • The modes of chemical decomposition of water by gamma rays, which underlie the variety of radiation-chemical effects observed in aqueous solutions of all kinds, have been considerably clarified in detail. Radiation decomposes water into the molecules H 2 a n d H 2 0 and t h e free radicals H a n d OH, the radicals being unobservable directly and their existence and number inferred from the chemical changes undergone by added solutes. • The absolute value of ferrous sulfate yield—important as the only practial check on the absolute accuracy of the standard cavity ion chamber method of gamma-ray dosimetry—is independent of radiation intensity over a wide range. T h e result is in good agreement with the latest colorim >tric values obtained elsewhere, but the accuracy is not much better than ±3%. • Studies of solutions of various polar compounds in hydrocarbons show that there are at least t w o modes of energy transfer from solvent to solute molecule which may b e quantitatively characterized: one appears to involve attack on the solute by free radicals, the second to b e identified with one or more of the three other processes mentioned above.
erties of sodium borohydride can be profoundly modified by addition of various polyvalent metal halides, they say in June 5 J ACS. t>AEC awards 24 research contracts, six new, the remainder renewals. Among the new are: Northwestern, Malcolm Dole, $14,846, Mechanism of High Energy Radiation Effects on Polyethylene; University of Pennsylvania, J. Bockris, $11,375, A Study of Structure of Molten Salts and Silicates; P u r d u e Research Foundation, J. W . Cobble, $22,800, Chemistry and Nuclear Chemistry of H e a v y Elements; University of Tennessee, J. F . Eastham, $3620, Determination and Application of Separation Factors for Some Chemical Fractionations of Hydrogen Isotopes. 2809
