Human acetylcholinesterase. Immunochemical studies with monoclonal antibodies

Monoclonal antibodies were used to investigate the immunochemistry of human erythrocyte acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7). A series of experiments on the sedimentation velocity and Stokes radius of acetylcholinesterase and its immune complexes indicated that each antibody recognized a single high-affinity binding site (epitope) on the monomeric enzyme. Further analysis suggested that the antibody-binding sites were replicated on multimeric enzyme forms but were subject to steric hindrance between nearby IgG molecules or adjacent enzyme subunits. The cellular localization of the epitopes was studied by measuring the binding of monoclonal antibodies to the cholinesterase of intact erythrocytes. The results implied that most of the epitopes are exposed to the external media. However, one antibody failed to bind to intact cells, despite a relatively high affinity for detergent-solubilized antigen, possibly because its epitope is buried in the lipid bilayer.     

Modulation of adenylate cyclase activity by sulfated glycosaminoglycans II. Effects of mucopolysaccharides and dextran sulfate on the activity of adenylate cyclase derived from various tissues

Heparin was found to be the most potent inhibitor of rat ovarian luteinizing hormone-sensitive adenylate cyclase (I₅₀ = 2 μg/ml) when compared to other naturally occurring glycosaminoglycans. This inhinibition was also appparent when this enzyme was stimulated by follicle-stimulating hormone or prostaglandin E ₂. Heparin was also found to inhibit glucagon-sensitive rat hepatice adenylate cyclase, and the prostaglandin E₁-sensitive enzyme from rat ileum and human platelets. In contrast, heparin stimulated the dopamine sensitive adenylate cyclase from rat caudate nucleus. The sulfade polysugar dextran sulfate exerts similar effects on adenylate cyclase activity of the rat ovary was shown to inhibit hormone binding to rat ovarian plasma membrane in a manner similar to that exerted by heparin. In contrast to heparin, dextran sulfate inhibited dopamine-sensitive adenylate cyclase from rat caudate nucleus.     

Reversal of the sarcoplasmic reticulum ATPase cycle by substituting various cations for magnesium. Phosphorylation and ATP synthesis when Ca2+ replaces Mg2+

Reversal of the cycle of sarcoplasmic reticulum ATPase starts from ATPase phosphorylation by Pi, in the presence of Mg2+, and leads to ATP synthesis. We show here that ATP can also be synthesized when Ca2+ replaces Mg2+. In the absence of a calcium gradient and in the presence of dimethyl sulfoxide, ATPase phosphorylation from Pi and Ca2+ led to the formation of an unstable phosphoenzyme. This instability was due to a competition between the phosphorylation reaction induced by Pi and Ca2+ and the transition induced by Ca2+ binding to the transport sites, which led to a conformation that could not be phosphorylated from Pi. Dimethyl sulfoxide and low temperature stabilized the calcium phosphoenzyme, which under appropriate conditions, subsequently reacted with ADP to synthesize ATP. Substitution of Co2+, Mn2+, Cd2+, or Ni2+ for Mg2+ induced ATPase phosphorylation from Pi, giving phosphoenzymes of various stabilities. However, substitution of Ba2+, Sr2+, or Cr3+ produced no detectable phosphoenzymes, under the same experimental conditions. Our results show that ATPase phosphorylation from Pi, like its phosphorylation from ATP, does not have a strict specificity for magnesium.     

Exploration of apical sodium transport mechanisms in an epithelial model by network thermodynamic simulation of the effect of mucosal sodium depletion: I. Comparison of three different apical sodium permeability expressions

A model based on that of Koefoed-Johnsen & Ussing (1958) and elaborated by Hviid Larsen (1978) and Lew et al. (1979), is designed using network thermodynamic theory and used to simulate experiments performed on epithelia. Three different expressions for the apical sodium permeability are tested for their ability to reproduce the saturation of the short-circuit current with increasing mucosal sodium concentration. Using the parameters from the previous models, the sodium entry step is shown to be the rate limiting step. If the apical sodium permeability is constant, there is no saturation of the short-circuit current with increasing mucosal sodium. The saturation of the short-circuit current is simulated with versions of the model which include a variable apical sodium permeability. The phenomenological expressions used for the variable permeabilities are those proposed by Fuchs et al. (1977) and Civan & Bookman (1982). They describe the so-called feedback effect of the mucosal and intracellular sodium concentrations.     

Education for sustainability in higher education: a multiple-case study of three courses

Education for sustainability (EfS) in higher education is an emerging specialisation within the general field of EfS. EfS encompasses cognitive, affective and behavioural aspects, and aims at enhancing a variety of learning outcomes in these domains and reaching students from all programmes. One of the main challenges for higher education educators is to design courses in a way that will effectively promote the various learning outcomes of EfS. A central question is how sustainability should be integrated into the curriculum; which topics should be taught and which pedagogies ought to be applied to improve students’ knowledge, skills and motivation to promote sustainable living. The present study aimed to contribute to the knowledge about students’ learning outcomes yielded by different designs of EfS courses. This multiple-case study of three courses used a mixed-methods design. For each course, we identified its characteristics and analysed students’ self-reported learning outcomes. We found that: (1) a course with a higher degree of participatory learning, employing a system approach, promoted the highest and most varied learning outcomes; (2) the lecture-based course yielded the fewest learning outcomes; and (3) field trips promoted learning outcomes only when accompanied by more advanced pedagogies.