Nicking by transesterification: the reaction catalysed by a relaxase

DNA relaxases play an essential role in the initiation and termination of conjugative DNA transfer. Purification and characterization of relaxases from several plasmids has revealed the reaction mechanism: relaxases nick duplex DNA in a site- and strand-specific manner by catalysing a transesterification. The product of the reaction is a nicked double-stranded DNA molecule with a sequestered 3'-OH and the relaxase covalently bound to the 5' end of the cleaved strand via a phosphotyrosyl linkage. The relaxase-catalysed transesterification is isoenergetic and reversible; a second transesterification ligates the nicked DNA. However, the covalent nucleoprotein complex is relatively long-lived, a property that is likely to be essential for its role as an intermediate in the process of conjugative DNA transfer. Subsequent unwinding of the nicked DNA intermediate is required to produce the single strand of DNA transferred to the recipient cell. This reaction is catalysed by a DNA helicase, an activity intrinsic to the relaxase protein in some, but not all, plasmid systems. The first relaxase-catalysed transesterification is essential for initiation of conjugative strand transfer, whereas the second is presumably required for termination of the process. The relaxase, in conjunction with several auxiliary proteins, forms the relaxation complex or relaxosome first described nearly 30 years ago as being associated with conjugative and mobilizable plasmids.     

The use of monochloroacetic acid for improved ethanol production by immobilized Saccharomyces cerevisiae

World Journal of Microbiology and Biotechnology -     

Metalloendoprotease inhibitors which block the differentiation of L6 myoblasts inhibit insulin degradation by the endogenous insulin-degrading enzyme

The cultured myoblasts of the rat skeletal muscle cell line L6 proliferate till confluency and then fuse to form myotubes and express a number of muscle-specific proteins. We had shown that this differentiation process is blocked by specific metalloendoprotease inhibitors. We now demonstrate that metabolizing L6 myoblasts and their cell extracts degrade insulin to acid-soluble fragments by a non-lysosomal pathway. About 90% of the insulin-degrading activity residues in the cytoplasm and is due to a 110-kDa enzyme known as the insulin-degrading enzyme. The same metalloendoprotease inhibitors that block the differentiation of L6 myoblasts also inhibit insulin degradation by the metabolizing L6 cells, their cell extracts, and the insulin-degrading enzyme immunoprecipitated from the cytosolic extracts by a monoclonal antibody. These results suggest that the insulin-degrading enzyme is the metalloendoprotease whose activity is required for the initiation of the morphological and biochemical differentiation of L6 myoblasts.     

A Model of Glutamate Neurotoxicity and Mechanisms of the Development of the Typical Pathological Process

Biophysics - A glutamate model of stroke was analyzed from the standpoint of the development of a typical pathological process that is thought to occur when major regulatory mechanisms are...     

The changing landscape of the clinical value of the PM/Scl autoantibody system

Autoantibodies to the polymyositis/scleroderma (PM/Scl) complex have been associated with systemic sclerosis and PM/Scl overlap syndrome. The report of Hanke and colleagues in a recent issue of Arthritis Research and Therapy is the first to describe the separate evaluation of anti-PM/Scl-75c and PM/Scl-100 autoantibodies and their relationship to clinical manifestations of systemic sclerosis. Several observations are of paramount interest, but are not in general agreement with earlier studies. These include the prevalence of anti-PM/Scl antibodies in systemic sclerosis, the association with certain clinical manifestations and prognosis of patients. This report will hopefully trigger systematic multi-centre studies to confirm and/or elucidate the novel line immunoassay and clinical associations.     

Enhanced reactivity to pain in patients with rheumatoid arthritis

Introduction  

Maladaptive physiological responses to stress appear to play a role in chronic inflammatory diseases such as rheumatoid arthritis (RA). However, relatively little stress research in RA patients has involved the study of pain, the most commonly reported and most impairing stressor in RA. In the present study, we compared psychophysical and physiological responses to standardized noxious stimulation in 19 RA patients and 21 healthy controls.