Steven Gutteridge

Identification of a critical region in the Drosophila ryanodine receptor that confers sensitivity to diamide insecticides.

Anthranilic diamides, which include the new commercial insecticide, chlorantraniliprole, are an exciting new class of chemistry that target insect ryanodine receptors. These receptors regulate release of stored intracellular calcium and play a critical role in muscle contraction. As with insects, nematodes express ryanodine receptors and are sensitive to the plant alkaloid, ryanodine. However the plant parasitic nematode, Meloidogyne incognita, is insensitive to anthranilic diamides. Expression of a full-length Drosophila melanogaster ryanodine receptor in an insect cell line confers sensitivity to the receptor agents, caffeine and ryanodine along with nanomolar sensitivity to anthranilic diamides. Replacement of a 46 amino acid segment in a highly divergent region of the Drosophila C-terminus with that from Meloidogyne results in a functional RyR which lack sensitivity to diamide insecticides. These findings indicate that this region is critical to diamide sensitivity in insect ryanodine receptors. Furthermore, this region may contribute to our understanding of the differential selectivity diamides exhibit for insect over mammalian ryanodine receptors.

A phosphatase from chloroplast stroma of Nicotiana tabacum hydrolyses 2′‐carboxyarabinitol 1 ‐phosphate, the natural inhibitor of Rubisco to 2′‐carboxyarabinitol

An enzyme has been identified in the stroma of tobacco chloroplasts that degrades the natural inhibitor of Rubisco, 2′‐carboxyarabinitol 1‐phosphate (2CA1P). The products of the catalysis, determined by HPLC and phosphate analysis are 2′‐carboxyarabinitol and inorganic phosphate indicating that the enzyme is a phosphatase. The only other phosphate esters found to be degraded by the enzyme were the branched‐chain carboxylic sugar bisphosphates, 2′‐carboxyarabinitol and ribitol 1,5‐bisphosphates that were converted to the corresponding 5‐monophosphates. Other intermediary metabolites of the photosynthetic cycle were essentially unaffected by the phosphatase. The kinetic parameters of the enzyme are consistent with those required to relieve the inhibition of rubisco in vivo.

Tubulin modulating antifungal and antiproliferative pyrazinone derivatives

A novel class of synthetic tubulin polymerization disruptors, based on a substituted pyrazin-2-one core, has been discovered. These molecules have proven to be potent broad spectrum fungicides, with activity on agriculturally important ascomycete and basidiomycete pathogens. They have also been found to be particularly potent against human rhabdomyosarcoma cells. Using an efficient synthetic route, the agricultural and medicinal activity was explored.

Some Mechanistic Aspects of Ribulose Bisphosphate Carboxylase

Water is involved in the carboxylase reaction in 2 distinct ways (Fig 1.) Besides its stoichiometric involvement, it hydrates both substrates. While carbon dioxide has long been recognised as the active species, no information is yet available on how the enzyme handles the geM-diol form of RuBP. The equilibria and kinetics of interconversion of the keto and gem-diol forms of RuBP have been studied by NMR and UV spectroscopy. As Table I indicates the equilibrium is temperature dependent, higher temperatures favoring the keto form.

The structure of the naturally occurring inhibitor of rubisco that accumulates in the chloroplast in the dark is 2′-carboxyarabinitol-1-phosphate

A whole range of plants exhibit, to a greater or lesser extent, diurnal regulation of the activity of Rubisco (1–4). This process in at least three plant species, potato, tobacco and Phaseolus is due to the synthesis of a potent inhibitor of rubisco that rapidly accumulates in the chloroplast stroma with the onset of darkness. The inhibitor is a monophosphate (2,3) that preferentially binds to the activated form of the enzyme, retaining it in this state throughout the dark period. Equally dramatic is the rate of restoration of full catalytic activity within some 60 minutes with the exposure of the leaf to light.