Antisera to the Coupling Factor of Photophosphorylation and Its Subunits

Stroma-freed chloroplasts were extracted with sucrose palmitate-stearate containing buffer. After the addition of dodecyl sulfate and mercaptoethanol to the extract a series of polypeptides was isolated from the mixture by gel filtration. These polypeptides were later used for immunization. Antisera to four polypeptides reacted in the Ouchterlony double diffusion test with authentic coupling factor yielding a precipitation band. According to the observed apparent molecular weights the polypeptides are the α, β , δ and ε subunits of the coupling factor. An antiserum to the γ subunit has been obtained already previously. All antisera inhibit photophosphorylation reactions and electron transport considerably. Addition of gramicidin inhibits photophosphorylation completely whereas gramicidin restores electron transport in the assays with the antisera to the α, β , γ and δ subunit. In the case of the antiserum to the ε subunit gramicidin does not regenerate electron transport. As in the presence of the serum to the ε subunit pH changes in the suspension medium are not observed, this serum seems to open a proton channel. Also, upon addition of dicyclohexyl carbodiimide (DCCD) pH changes in the suspension medium in the assay with antiserum do not reoccur. According to these unexpected results the identity of the antigen with the ε subunit of the coupling factor is not certain. ATP-ase reactions are only inhibited by the antisera to the α and γ subunit and what is thought to be the ε subunit. The antiserum to the α subunit uncouples electron transport as the only one when used in sufficient concentrations. The dosis-effect curves of the inhibition of the electron transport exhibits a maximum. The dosis-effect curves for the other components rise after a lag phase in an approximately hyperbolic manner. The inhibitory action on electron transport is exerted by all antisera in the region of the reaction center I or in its immediate vicinity. This is thought to be due to the fact that a protein of the reation center I is inhibited in its function by the increasing proton concentration inside the thylakoid. The inhibition of electron transport by the antiserum to the ε subunit is considered to be a direct serum effect. Besides the increase in fluorescence yield, due to the inhibition of electron transport in the region of photosystem I, decreases of the fluorescence yield are observed in the presence of DCMU, which do not depend on the redox state of Q but rather on the condition of the thylakoid mem­brane. Moreover, the antisera affect in a differing manner the energy spill-over of excitation from photosystem II to photosystem I.

Regulation of ribosomal RNA synthesis in Tetrahymena pyriformis

Ribosomal RNA is synthesized at constant rate during most of the cell cycle in heat-shock synchronized populations of Tetrahymena pyriformis. Early in each macronuclear S-period the rate of synthesis increases abruptly, concomitant with replication of the genes coding for ribosomal RNA. The increase is prevented by inhibitors of DNA replication, added prior to the S-period. Similarly, in cultures synchronized by starvation/refeeding, inhibition of DNA replication, at the time when the rDNA is replicated, will prevent the normal increase in rate of RNA synthesis which follows refeeding. We conclude that inhibition of rDNA replication interferes with the synthesis of rRNA, and we suggest that with respect to rRNA synthesis a gene dosis effect is operating in fast-growing Tetrahymena cells.

Über die Wirkung von β-Strahlen auf die Photosynthese-Phosphorylierung und die Hill-Reaktion isolierter Chloroplasten

Isolated spinach chloroplasts were exposed to ionising radiation (β-rays) from 90Sr. After irradiation photosynthetic-phosphorylation (PP) and Hill - reaction (HR) were checked and found to have high, but markedly different resistance. Dosis effect-curves were found indicating fifty percent inactivation of 130 000 rad (PP) or 530 000 rad (HR) respectively. There was no special effect of temperature on radiation resistance of the susceptible photosynthetic-phosphorylation. Results are discussed regarding their bearing upon the theory of radiation effects and upon the primary processes of photosynthesis.