Kinetic properties of F0F1-ATPases. Theoretical predictions from alternating-site models.

We present an analysis of models based on current structural concepts of the F0F1 synthases, accounting for coupling between proton transport and ATP synthesis. It is assumed that each of the three alpha beta-subunits of the synthase can exist in three different conformational states E, Eo and E*. Proton translocation is coupled to cyclic interconversion of the conformations of the alpha beta-subunits. The conformational changes of these subunits are assumed to be coordinated so that all three interconvert simultaneously, in a rate-limiting transition. Binding and release of the ligands ATP, ADP, Pi, and protons are assumed to be equilibrium steps. In one family of models, interconversion of the alpha beta-subunits of F1 is coupled to the translocation event in F0 acting as a proton carrier. In a second family of models, protons combine with F0F1 and are translocated during the interconversion step in a chemiport. Kinetic tests involving the mutual effects of [ATP], [ADP], H+', and H+" are described, allowing us to make a distinction between the different models and submodels.     

Analysis of a model for antagonistic muscles

In the present work a linear model for a pair of antogonistic muscles is analysed. Each constituent muscle in this model is identical to ones considered previously (Stein and Ouztöreli, 1976). Analytical properties of the antagonistic muscles and dynamics of the system are described and some numerical results are discussed. The natural modes of the system are determined by a fourth order polynomial, which most commonly has one pair of conjugate complex roots and two negative real roots. The filtering of neural inputs through the active state properties of the muscle increases the order of the system to fifth order for these inputs.This work was partly supported by the National Scientific and Engineering Research Council of Canada Grant NRC-A4345 and by the Medical Research Council of Canada Grant MRC-MT-3307 through the University of Alberta     

Effect of abscisic acid on CO2 exchange in Lemna gibba

The effects of abscisic acid (ABA) on photosynthesis, dark respiration, and photorespiration were studied in Lemna gibba L. plants. The initial concentration of ABA in the nutrient solution was 10⁻⁷M and in a few experiments, 10⁻⁶M. The cultures were grown in the same solution for time periods ranging from one hour to 12 days. Net photosynthesis, measured as CO₂ uptake by infrared gas analyser technique, was inhibited after four hours of ABA treatment and reached a minimum after four to seven days depending on the time of the year. After 12 days a substantial recovery of photosynthesis was observed. Dark respiration was significantly stimulated after two to seven days of ABA treatment but then returned to the control level. The transient effects of ABA on photosynthesis and dark respiration corresponded to the previously measured time course of [¹⁴C]-ABA uptake by Lemna . Photorespiration measured as oxygen inhibition of photosynthesis was not affected by ABA.     

Identification of the Low Molecular Weight Copper Protein from Copper-intoxicated Mung Bean Plants

Mung bean plants (Wilczek) accumulate increasingly greater amounts of buffer-extractable copper in both their shoots and roots when grown in liquid medium containing greater than 2 micrograms per milliliter copper (31.4 micromolar) as cupric sulfate. This increase in soluble copper is accompanied by an increase in the relative amount of low molecular weight (7,000 to 20,000) macromolecular-bound copper and a decrease in the relative amount of high molecular weight (greater than 20,000) copper. The major low molecular weight copper protein has been isolated from copper-intoxicated mung bean plants by a combination of ammonium sulfate fractionation, gel filtration, and ion exchange chromatography. It was identified as mung bean plastocyanin on the basis of its molecular weight, optical behavior, and amino acid composition. No evidence was found for a low molecular weight copper-binding protein corresponding to mammalian thionein or chelatin.     

The bacterial origin of rat breath pentane

Vitamin E-deficient rats or rats subjected to other conditions thought to lead to peroxidation of tissue lipids produce pentane and other hydrocarbon gases in the breath. However, pentane production is found to depend on the linoleate content of the recent diet. It is decreased or eliminated by inclusion of ascorbic acid in the food or water, by removal of linoleate from the diet, by starvation and by the antibiotic, clindamycin. It is enhanced by feeding linoleate hydroperoxide or by removal of vitamin E from the diet for a short period. These findings lead to the conclusion that the major source of pentane is not membrane lipid peroxidation but is from the action of intestinal bacteria on linoleate hydroperoxide.