Factors controlling ATP levels during photophosphorylation catalyzed by Rhodospirillum rubrum chromatophores

Summary Photophosphorylation of ADP catalyzed by chromatophores represents a possible method for regenerating ATP from ADP for use in large-scale enzymatic synthesis of complicated molecules. We found that the extent of conversion of ADP to ATP in the presence of ascorbate and magnesium chloride was influenced by the presence of bubbling gas in contact with the reaction mixture, and by the presence of fumarate: with no fumarate or gas contact, low conversions (usually about 50%) were obtained; however, under the same conditions, but in the presence of fumarate or bubbling gas, 100% conversions were obtained. We discuss mechanistic implications of our findings.     

Preparation and properties of bacterial chromatophores entrapped in polyacrylamide

The immobilization of Rhodospirillum rubrum chromatophores was successfully performed by entrapping them in polyacrylamide. Their photophosphorylating activity was about 40% of native chromatophores. The temperature and pH optima for immobilized chromatophores were similar to the native photosynthetic apparatus and kinetic parameters showed that the rate of photophosphorylation in polyacrylamide particles was diffusion controlled. Light penetration of the gel particles was not a limiting parameter. Immobilization considerably increased the stability of the chromatophores towards denaturation.     

Synergistic interaction between prostaglandins and paf-acether in experimental animals and man

Platelet activating factor (PAF-acether) is released from a variety of inflammatory cell types and has properties appropriate to a mediator of allergy and inflammation. Here, we have examined the interaction between PAF-acether and the prostaglandins, PGE2 and ZK 36374 (a stable analogue of prostacyclin, PGI2) in the skin of guinea-pigs and human volunteers. PGE2 and ZK36374 significantly potentiated increased plasma protein extravasation induced by PAF-acether in guinea-pigs, assessed by extravasation of I-125-HSA. In addition, PGE2 significantly potentiated the ability of PAF-acether to elicit acute wheal (volume) and flare responses in human skin. The inflammatory properties of PAF-acether should not be considered in isolation since this phospholipid interacts synergistically with prostaglandins which are recognised as modulators of inflammation.     

Purification of acetate kinase by affinity chromatography.

A one-step procedure using affinity chromatography has been shown to purify to apparent homogeneity acetate kinase from a commercially available preparation and to partially purify the enzyme from a crude, cell-free extract. Since the gel's capacity for enzyme adsorption is controlled by the thermodynamics of ligand-enzyme interaction, maximization of the adsorption isotherm was attempted. Enzyme adsorption decreased logarithmically with increasing ionic strength but increased with increasing concentration of MgCl2. These competing effects caused the net adsorption of enzyme to increase to a maximum and then to decrease as the MgCl2 concentration was raised. The results allow a significant improvement in affinity column performance and have important implications for scale-up procedures.     

Testosterone and behaviour during extinction in chicks

Testosterone-injected and control male chicks, in their second week of life, were observed during eight (massed) 1-min extinction trials of a runway response for a food reward. The hormone produced no overall differences in extinction rates but the following changes in behaviour were observed: first, increased frequency of contact with the empty food dish (pecking the outside, scratching, and treading); secondly, increased frequency of fixated gazing at the walls; thirdly, decreased looking up from the runway; and fourthly, increased head shaking. These results were discussed in relation to effects of testosterone on attack and attention.