EZ-FIT: a practical curve-fitting microcomputer program for the analysis of enzyme kinetic data on IBM-PC compatible computers

Effect of grafted polyethylene glycol (PEG) on the size, encapsulation efficiency and permeability of vesicles.

Competitive binding of vascular cell adhesion molecule-1 and the HepII/IIICS domain of fibronectin to the integrin alpha 4 beta 1.

The interaction of some pesticides and herbicides with humic substances

Tonoplast vesicles were prepared from leaf mesophyll homogenates of the crassulacean-acid-metabolism plant Kalanchoe daigremontiana Hamet et Perrier de la Bâthie to study the effects of anions on ATP- and inorganic-pyrophosphate (PPi)-dependent H+ transport. In the presence of gramicidin, substrate hydrolysis by the tonoplast ATPase was characteristically stimulated by chloride and inhibited by nitrate, but was unaffected by malate and a wide range of other organic-acid anions; the PPiase was anion-insensitive. Malate was more effective than chloride both in stimulating ATP- and PPi-dependent vesicle acidification (measured as quinacrine-fluorescence quenching) and in dissipating a pre-existing inside-positive membrane potential (measured as oxonol-V-fluorescence quenching), indicating that malate was more readily transported across the tonoplast. Certain other four-carbon dicarboxylates also supported high rates of vesicle acidification, their order of effectiveness being fumarate ≫ malate ∼-succinate > oxalacetate ∼- tartrate; the five-carbon dicarboxylates 2-oxoglutarate and glutarate were also transported, although at lower rates. Experiments with non-naturally occurring anions indicated that the malate transporter was not stereospecific, but that it required the trans-carboxyl configuration for transport. Shorter-chain or longer-chain dicarboxylates were not transported, and neither were monocarboxylates, the amino-acid anions aspartate and glutamate, nor the tricarboxylate isocitrate. The non-permeant anions maleate and tartronate appeared to be competitive inhibitors of malate transport but did not affect chloride transport, indicating that malate and chloride influx at the tonoplast might be mediated by separate transporters.

Proton and anion transport at the tonoplast in crassulacean-acid-metabolism plants: specificity of the malate-influx system in Kalanchoë daigremontiana.

A.G. Lowe

Papers

Multifit: a flexible non-linear least squares regression program in BASIC.