Phosphonate biosynthesis: isolation of the enzyme responsible for the formation of a carbon-phosphorus bond

The first isolation of a naturally occurring phosphonate in 1959 led rapidly to the discovery of a variety of metabolites containing a phosphorus-carbon bond. Phosphonates have been found in bacteria, fungi, and higher organisms such as the snail schistosome vector Biomphalaria. The biosynthetic path to the P-C bond has, however, remained undefined. Thus although it was shown twenty years ago that the isotope label from [14C]glucose or from [32P]phosphoenolpyruvate is incorporated into 2-aminoethylphosphonate by the protozoan Tetrahymena pyriformis, the presumed stoichiometric transformation of phosphoenolpyruvate to phosphonopyruvate has never been demonstrated. Low conversions of phosphoenolpyruvate into 2-aminoethylphosphonate and the trapping of phosphonopyruvate from phosphoenolpyruvate have been reported, but these reactions have not proved reproducible, and the existence of the critical enzyme, phosphoenolpyruvate phosphonomutase, has remained notional. We now report experiments that resolve this enigma, and describe the isolation and characterization of the pure mutase from T. pyriformis.     

Change in pattern of ongoing cortical activity with auditory category learning

Humans are able to classify novel items correctly by category; some other animals have also been shown to do this. During category learning, humans group perceptual stimuli by abstracting qualities from similarity relationships of their physical properties. Forming categories is fundamental to cognition and can be independent of a 'memory store' of information about the items or a prototype. The neurophysiological mechanisms underlying the formation of categories are unknown. Using an animal model of category learning, in which frequency-modulated tones are distinguished into the categories of 'rising' and 'falling' modulation, we demonstrate here that the sorting of stimuli into these categories emerges as a sudden change in an animal's learning strategy. Electro-corticographical recording from the auditory cortex shows that the transition is accompanied by a change in the dynamics of cortical stimulus representation. We suggest that this dynamic change represents a mechanism underlying the recognition of the abstract quality (or qualities) that defines the categories.     

Possible regulatory function of acetylcholine receptor in maintenance of retinotectal synapses.

alpha-Neurotoxins bind to cholinergic receptor, block transmission, and induce sprouting of retinal terminals in the toad tectum. New connections retain an orderliness that suggests a selective affinity between presynaptic terminals. The results suggest that postsynaptic cells exert a control, associated with receptors, on the growth of presynaptic terminals and on the maintenance of their synaptic connections.