Site-directed mutagenesis reveals role of mobile arginine residue in lactate dehydrogenase catalysis

The binding of substrates to lactate dehydrogenases induces a marked rearrangement of the protein structure in which a 'loop' of polypeptide (residues 98-110) closes over the active site of the enzyme. In this rearrangement, arginine 109 (a basic residue conserved in all known lactate dehydrogenase sequences and in the homologous malate dehydrogenases) moves 0.8 nm from a position in the solvent to one in the active site where its guanidinium group resides within hydrogen bonding distance of both the reactive carbonyl of pyruvate and imidazole ring of the catalytic histidine 195 (see Fig. 1). Whilst this feature of the enzyme has been commented upon previously, the function of this mobile arginine residue during catalysis has not been tested experimentally. The advent of protein engineering has now enabled us to define the role of this basic residue by substituting it with the neutral glutamine. Transient kinetic and equilibrium studies of the mutant enzyme indicate that arginine 109 enhances the polarization of the pyruvate carbonyl group in the ground state and stabilizes the transition state. The gross active-site structure of the enzyme is not altered by the mutation since an alternative catalytic function of the enzyme (rate of addition of sulphite to NAD+), which does not require hydride transfer, is insensitive to the arginine----glutamine substitution.     

On creating opportunity out of conflict: Two case studies

This paper discusses Interactive Planning and Management (Ackoff, 1981) and its value for managing creatively and effectively in conflict situations. The author compares and contrasts the approach with alternative dispute resolution (ADR) including mediation-, negotiation-, and litigation-based processes and argues that the current methods developed in the ADR field are inadequate in their design to accommodate four considerations: (1) the interrelationships of problems facing organizations in conflict, (2) the accelerating rate of change in society, (3) the purposefulness of the parts of social systems as well as of the systems themselves, and (4) the effects of organizations' actions on their environment. The paper presents two cases in which Interactive Planning and Management was used to transform organizational decision making and structure.