Volume 18, Issue 9

A biochemical approach to the study of photosynthesis in terms of hydrogen transport is described. In particular, the system concerned with reduction of the coenzymes has been found to depend on two proteins: a non haem iron protein closely connected with a photochemical reaction and a flavoprotein which acts as a reductase. The iron protein, previously known as “methaemoglobin reducing factor” and as “photosynthetic pyridine nucleotide reductase”, is recognised as a member of a class of proteins now called ferredoxin.

The role of chloride in photosynthetic oxygen evolution was reinvestigated by determining the effect of this ion on photochemical reactions of chloroplasts in which oxygen either is or is not produced. The chloroplasts used were isolated from normal spinach leaves. The level of chloride in the reaction mixture was controlled by washing the isolated chloroplasts and by avoiding a chloride contamination from the water and chemicals used. Chloride was found to be essential for each of the photochemical reactions of chloroplasts in which oxygen is produced. These included (a) photoreduction of TPN, (b) photophosphorylation of the noncyclic type in which TPN or ferricyanide reduction is coupled with ATP formation and (c) photophosphorylation of the aerobic, “pseudocyclic” type in which oxygen production occurs but is masked by an equal oxygen consumption. No chloride requirement was found for the anaerobic, cyclic photophosphorylation in which oxygen is not produced. These results support the view that chloride is an essential cofactor for oxygen evolution in photosynthesis.

Chloroplasts illuminated at p H 6 accumulate a limited amount of “XE” — an unidentified component which can phosphorylate ADP in a dark reaction at p H 8. The maximum formation of XE requires 15 to 30 seconds’ light if a cyclic cofactor is present, and otherwise as much as 4 minutes’ light. Ferricyanide and cyclic cofactors provide the highest XE yields, with other cofactors giving a lower value. The cofactorless system appears to have two components of which one is ascorbate dependent. The results suggest that XE is located at or near the phosphorylation site as studied in one stage photophosphorylation at p H 8.

Photosynthetic reactions of petrolether-extracted chloroplasts were investigated. The photosynthetic reduction of NADP by plastoquinone-free chloroplasts can be reactivated by addition of dimethylsubstituted p-benzoquinones with a side-chain of at least one isoprene unit. Broken chloroplasts. from which plastoquinone has been only partly extracted, are able to reduce NADP and p-benzoquinones, but not ferricyanide, o-quinones, vitamin K 3 and anthraquinone-sulfonate. The interpretation of these results as two functions of plastoquinone in photosynthetic electron transport is critically discussed.

Uniformly labelled radioactive glucose was fed to Chlorella cells in the presence of non-radioactive carbon dioxide. The concentration of carbon dioxide was varied and the distribution of radioactivity determined in the light. At low concentrations of carbon dioxide much of the radioactivity appeared in glycollate or derivatives thereform. By contrast, at higher concentrations of carbon dioxide, most of the radioactivity appeared in sucrose. If the concentration of oxygen was increased above that normally present in air, there was relatively more activity in glycollate. The effect of the addition of isoniazid in these conditions was also investigated. It was concluded that glucose fed to Chlorella exogenously is metabolised in the light in Chlorella via sugar phosphate intermediates of the Calvin cycle.

Extracts of the blue-green alga Anacystis nidulans could be fractionated by countercurrent distribution using petroleum ether as the “mobile” and a methanol : water (94 : 6) mixture as the “stationary” phase.

The stoichiometry of photosynthesis has been estimated with spinach chloroplasts isolated under conditions in which the loss of protein during the washing procedure can be avoided. The TPN-reduction is definitely higher as described in literature. Without further addition of exogenous enzyme or extract the chloroplasts from primary leaves reduce 100 —200 µmoles TPN/mg chlorophyll and hour. In air the TPNH-value is 20—30% lower as in nitrogen. However, compared to the high TPNH-concentration the ATP-level is too low. The ATP-concentration increases by addition of ascorbate whereas this has no influence on the TPN-reduction. Without further addition of ascorbate the stochiometry TPNH : ATP : O is 2:1:2. The low ATP-value is only partly due to an ATPase. The difference cannot be explained by the presence of this enzyme. Even in presence of ascorbate and with the calculation of the activity of the ATPase we never estimated the theoretically required value.

The changes in the concentrations of FDP *, DAP, PGA, RuDP, PEP, Pyruvat, ADP and ATP in Chlorella occuring during the transition from light to dark and from dark zu light were enzymaticaly determined. Moreover after a period of photosynthesis, the rate of 14 CO 2 dark-fixation and the distribution of 14 C in the intermediates were determined. During the first few sec after illumination in air+CO 2 FDP, DAP and ATP increase. while PGA, PEP and ADP decrease. The opposite changes are observed during the light-dark-change. The pronounced increase in PGA is practically linear during the first 6 sec after the illumination is discontinued. When comparing to the CO 2 fixation rate of the preceding period of photosynthesis no stoichiometrical relationship was obtained. Depending on the rate of photosynthesis CO 2 /PGA ratios between 0.3 and 3.5 were obtained. Absence of CO 2 has no measurable influence on the rate of PGS formation after turning off the light, where as under N 2 the formation of PGA is completely inhibited. It is concluded that the big changes in the concentration of the intermediates are caused by a competition of light phosphorylation with glycolysis for the inorganic phosphate anologous to the Pasteur effect in yeast. Beginning of illumination means beginning of light phosphorylation and decrease in the concentration of ΡΟ 4 3⊖ and thus inhibition of triose oxidation. As a consequence PGA and PEP drop, while DAP and FDP accumulate. When illumination stops, light phosphorylation stops and thus ΡΟ 4 3⊖ is increased and triose oxidation is accelerated. The result is a fast increase in PGA and a decrease in FDP and DAP. A small part of the PGA formed after turning off the light originates from the reaction of RuDP with CO 2 . It is assumed, that the carboxylation product of RuDP participating in photosynthesis is not identical with free PGA with which it therefore is not at equilibrium. By hydrolysis of the carboxylation product during extraction or after darkening, however, free PGA is formed.

The discovery of the active group of the hydrogen-transferring enzymes — nicotinamide — for which OTTO WARBURG was nominated by the Nobel Committee 1 “for a prize for the second time in 1944, when he again was found to deserve the honor”, has had a profound influence on all of biochemistry. The present paper describes a fundamental inhibition of intracellular tumor metabolism produced by reduced diphosphopyridine nucleotide (DPNH 2 ) added extracellularly.

Der Mechanismus der Abtötung von Ascites-Krebszellen durch Clostridium butyricum wurde untersucht. Die Abtötung wurde zurückgeführt auf Wasserstoffperoxyd, das sich in den vegetativen Clostridien bildet, wenn sie mit Luftsauerstoff in Berührung kommen.

Acetate-[1- 14 C] and cinnamic acid-[3- 14 C] were administered to young leaves of Gaultheria procumbens L. The methylsalicylate isolated from the essential oil was radioactive only with cinnamic acid-[3- 14 C] as the precursor. Decarboxylation of the salicylic acid showed that the total radioactivity was located in the carboxyl group. Salicylic acid must therefore be regarded as a metabolite of cinnamic acid.

Es werden die spez. Radioaktivitäten von Purinen und Leucopterin aus Kohlweißlingen, denen Glycin-[2- 14 C] sowie Amino-imidazol-carboxamid-[4- 14 C] zu verschiedenen Zeiten der Puppenruhe appliziert worden war, verglichen. Aus diesen Ergebnissen wird geschlossen, daß eine Umwandlung der Purine in Leucopterin mit einem Minimum an struktureller Änderung erfolgt. Die hohen Einbauraten für 14 C-markierte Ribonucleinsäuren, Adenyl- und Guanylsäure bestätigen diese Annahme. Bei Gabe von Ribose-[1- 14 C] ergibt sich bei kurzer Verweilzeit eine hohe Einbaurate in Leucopterin. Das Aktivitätsverhältnis von C-8 : C-9 * ist dann 14 : 86. Der Mechanismus des Überganges Purin → Pterin wird diskutiert. — In den Kohlweißlingen wurde neben den üblichen Purinen noch Isoguanin und 2.8-Dihydroxy-guanin nachgewiesen.