Synthesis of amodel system for the primary energy conversion reactions in photosynthesis

A model system is constructed which, like the photosynthetic apparatus of green plants, can convert light to chemical free energy through pigment-sensitized photooxidation of water. The system has two light-harvesting subunits connected electrically in series. Each subunit is made of a multimolecular layer of Zn(II)-tetraphenylporphyrin deposited on a clean aluminum surface and immersed in an aqueous mixture of potassium ferri- and ferrocyanide. Upon illumination by amber light, charge transfer takes place across more than 70 molecular layers of the pigment with a photoelectromotive force of 1.1 to 1.3 volts per subunit. With NADP as the electron acceptor and NADP-reductase as a mediator, the system can photooxidize water to oxygen gas. With these model experiments as a guide, a molecular mechanism for the primary energy conversion reactions in photosynthesis is formulated that offers a unified interpretation of most of the relevant observations reported in the literature.

The influence of growth phase and ionic environment on the dissociation of Escherichia coli ribosomes by p-chloromercuribenzoate

The effect of p-chloromercuribenzoate (PCMB) on the structure of polysomes and ribosomes isolated from early log phase and stationary phase cells of Escherichia coli B has been studied in the presence and absence of K+. At 0° no breakdown of polysomes was observed in the presence of 0.5 mM PCMB. The 100S dimer, however, both at 0° and 25°, was readily dissociated under all conditions tested. The dissociation of 70S particles was much more sluggish and was most apparent in ribosomes isolated from early log phase cells in buffer containing K+. These results indicate that the sulfhydryl groups involved in 100S dissociation are more accessible to PCMB than those involved in the dissociation of 70S particles.