Electron-paramagnetic-resonance studies on cobalt(II) carbonic anhydrase–sulphonamide complexes

Sulphonamide adducts of three Co(II) carbonic anhydrases were investigated by e.p.r. (electron paramagnetic resonance) at helium temperatures. The highly anisotropic 9 GHz spectra exhibited only three distinct features, with g values between 6.3 and 1.5. Such spectra arise from an electronic state with effective spin S'=(1/2), indicating that the high-spin (S=3/2) ground level is split into two spin doublets differing in energy by an amount large compared with the microwave quantum, but small in relation to thermal energies at ambient temperature. This situation would occur in a tetrahedral system suffering a large rhombic distortion. Calculations based on this model accounted for apparent discrepancies in integrated spectral intensities, and yielded magnetic moments in good agreement with independent measurements, especially in the case of certain small Co(II) complexes resembling the enzyme adducts in their e.p.r. signals. Precise sets of g values, reflecting a particular co-ordination geometry, were found to be representative of each enzyme variant and the type of sulphonamide inhibitor, whether benzocyclic or heterocyclic. A series of substituted benzene sulphonamides bound to the same enzyme gave rise to closely similar spectra despite a wide range of pK(i) values. Thus benzocyclic and heterocyclic sulphonamides were evidently held in the active-site cleft in characteristic orientations irrespective of side chains that might considerably influence the total binding strength. Visible absorption spectra of various sulphonamide adducts at room temperature showed a similar pattern of inhibitor dependence to the e.p.r. spectra, suggesting a correspondence between the co-ordination structures in liquid and frozen solution. E.p.r. spectra of the sulphonamide complexes were remarkable not only for their range of g values, but also for their variations in line-width and spin-lattice relaxation behaviour. Addition of glycerol to the medium produced marked enhancement in resolution, owing to the creation of a more homogeneous frozen matrix. The non-uniform spin relaxation was probably a consequence of the large anisotropy in effective g tensor.     

Metabolic Regulation by Homoserine in Escherichia coli B/r

A mathematical analysis of branched pathway regulation has led to the prediction of a novel homoserine control in Escherichia coli B. Experimental support for such control is presented in this paper. Homoserine, the precursor of both threonine and methionine, inhibits nicotinamide adenine dinucleotide phosphate (NADP(+))-specific glutamate dehydrogenase (EC 1.4.1.4), the enzyme catalyzing the first reaction in ammonia assimilation. Physiological and biochemical evidence for this effect are offered. Homoserine depresses the growth rate of the organism, and glutamate, the product of the inhibited reaction, reverses this effect. The NADP(+)-specific glutamate dehydrogenase activity in cell-free extracts is inhibited by homoserine, and this inhibition parallels the restriction of growth rate. These effects are found in other enteric bacteria which share a similar overall pattern of control for the amino acids derived from aspartate. On the other hand, a sampling of more distantly related species which have different pathways and/or regulatory patterns provides no evidence for homoserine inhibition of the glutamate dehydrogenase reaction.     

Simple Medium for Pigment Production by the Erythrasma Diphtheroid

A simple method for the isolation and identification of the causative diphtheroid of erythrasma, Corynebacterium minutissimum, utilizes Muiller-Hinton Agar.     

A note on the diffusion approximation for single neuron firing problems

Summary This paper presents a well-known stochastic model used to describe the firing or discharge pattern of a single neuron in terms of various input processes, and shows how the potential level of the neuron can be given by means of a diffusion equation approximation. There is a discussion of the adequacy of this approximation, and the paper concludes with a brief discussion of first passage time problems.Supported in part by a grant from the Alfred P. Sloan Foundation to the Committee on Mathematical Biology and by a grant of the Statistical Branch, Office of Naval Research to the Department of Statistics, University of Chicago.     

An Ion Displacement Membrane Model

The usual assumption in treating the diffusion of ions in an electric field has been that the movement of each ion is independent of the movement of the others. The resulting equation for diffusion by a succession of spontaneous jumps has been well stated by Parlin and Eyring. This paper will consider one simple case in which a different assumption is reasonable. Diffusion of monovalent positive ions is considered as a series of jumps from one fixed negative site to another. The sites are assumed to be full (electrical neutrality). Interaction occurs by the displacement of one ion by another. An ion leaves a site if and only if another ion, not necessarily of the same species, attempts to occupy the same site. Flux ratios and net fluxes are given as functions of the electrical potential, concentration ratios, and number of sites encountered in crossing the membrane. Quantitative comparisons with observations of Hodgkin and Keynes are presented.     

CONCENTRIC LAMINATION OF GLIAL PROCESSES IN OLIGODENDROGLIOMAS

Tissues were obtained by open biopsy of a series of human intracranial neoplasms, fixed in Veronal-buffered osmium tetroxide, and embedded in Vestopal-W. In two instances in which specimens were obtained from oligodendrogliomas in regions where the tumor had infiltrated but not entirely destroyed cortical tissues, glial processes were found to be arranged in a highly organized laminar fashion. This feature was not observed in two additional oligodendrogliomas nor in other types of intracerebral neoplasms. Three types of laminar structures were recognized: (a) perikaryal sheaths composed of several layers of overlapping or concentrically orientated glial processes, (b) layers of longitudinally orientated glial processes along the outer aspect of myelinated axons, and (c) small laminated figures composed of several concentrically disposed glial processes. Spirally constituted lamellar systems were not demonstrated. These findings indicate that under certain circumstances glial cells have the capacity to form sheaths and sheath-like structures by concentric lamination of several processes, rather than by spiraling of a single process.