Why modification of the LD50 test will not be enough

During the last 10 years, the 'Three Rs' (reduction, refinement and replacement) concept of alternatives has come to be widely accepted, and new national and international laws require that non-animal procedures should replace animal experimentation wherever possible. Some reduction and refinement of animal use in toxicity testing has been achieved, and non-animal methods are becoming widely used as prescreens. However, even replacing the LD50 test by a modified and validated animal test, the Fixed Dose Procedure, will be a major achievement. In this paper it is argued that this is not good enough, and that more effort must be put into the development, validation, acceptance and use of genuine replacement alternative tests.     

Concanavalin A will not assume the sugar binding conformation in the complete absence of metal ions

Concanavalin A (Con A) is known to exist in two conformations that differ in their capacity to bind metals and sugars. The conformation that binds metals tightly and has a high affinity for sugars is termed the “locked” form and the conformation with low affinity for sugars and binds metals weakly is termed the “unlocked” form. It has recently been reported [Brown, $\text{et al.}$ Biochemistry $\text{21}$, 465(1982)] that apo-Con A will form the locked conformation in the absence of metals to the extent of 12.5% when equilibrated at 25°C for one week. In this report we show that Con A will not assume the locked conformation in the complete absence of metals and that only trace amounts of Ca²⁺ can catalytically convert a significant amount of the protein into the locked conformation.     

To be, or not to be two sites: that is the question about LeuT substrate binding

Transport proteins of the neurotransmitter sodium symporter (NSS) family regulate the extracellular concentration of several neurotransmitters in the central nervous system. The only member of this family for which atomic-resolution structural data are available is the prokaryotic homologue LeuT. This protein has been used as a model system to study the molecular mechanism of transport of the NSS family. In this Journal Club, we discuss two strikingly different LeuT transport mechanisms: one involving a single high-affinity substrate binding site and one recently proposed alternative involving two high-affinity substrate binding sites that are allosterically coupled.