An extended kinetic analysis of valinomycin-induced Rb-transport through monoglyceride membranes.

The time course of the current following a voltage jump, which is applied to monoglyceride bilayers in the presence of valinomycin, shows two relaxation times. This is basically in agreement with a simple carrier model which has been described in full detail formerly. Relaxation times and amplitudes allow a calculation of the rate constants of the transport model. The presented data supplement an analysis which was hitherto based only on the slower relaxation process and on information derived from the nonlinearity of current-voltage characteristics. The additional resolution of the faster relaxation time allowed an approximate determination of the voltage dependence of the translocation rate constant for carrier-ion-complex and provided evidence for a small voltage dependence of the interfacial reaction. The dependence of the relaxation parameters on the ion concentration in the aqueous phase was interpreted assuming a saturation of the ion concentration at the reaction plane at high bulk concentrations.     

Metabolism of nicotinic acid in plant cell suspension cultures: II; Isolation, characterization and enzymology of nicotinic acid N-alpha-arabinoside (author's transl)]

A very hydrophilic compound was isolated from parsley cell suspension cultures in high yield after application of nicotinic acid. Using chemical, chromatographic and spectroscopic procedures the structure of this new plant constituent has been elucidated as nicotinic acid N-alpha-L-arabinopyranoside. This structure has been proved by chemical synthesis. An arabinosyltransferase was isolated from parsley cell suspension cultures and purified about 19-fold. The enzyme converted nicotinic acid N-alpha-arabinoside with UDP to nicotinic acid and UDP-arabinose. pH-Optimum (pH 7.0-8.0), Km value for nicotinic acid N-alpha-L-arabinoside (2.2 X 10(-4) mol/l) and mol. wt. (app. 70 000) of the transferase were measured. Function and biosynthesis of the arabinoside in cell cultures are discussed.     

Acetylene reduction by nitrogen-fixing blue-green algae

Summary Known nitrogen-fixing species of blue-green algae are capable of reducing acetylene to ethylene, but acetylene is not reduced by Anacystis nidulans, which does not fix nitrogen. Cycad root nodules which contain blue-green algae as endophytes reduce acetylene. Acetylene reduction is inhibited by carbon monoxide. Nitrate or ammonium-nitrogen has no immediate effect on algae reducing acetylene, but algae grown on nitrate-nitrogen gradually lose their capacity to reduce acetylene. Nitrate-nitrogen also inhibits heterocyst formation in these algae and there is a fairly direct correlation between the abundance of heterocysts in a particular sample and its capacity to reduce acetylene. Aphanizomenon flosaquae reduces acetylene and fixes nitrogen in unialgal culture and there is strong presumptive evidence that these reductions are carried out by the alga rather than by associated bacteria. The molar ratios of ethylene: ammonia produced vary within the range 1.4–1.8.