Iron transport in Escherichia coli: relationship between chromium sensitivity and high iron requirement in mutants of Escherichia coli

Utilization of iron (Fe(3+)) by Escherichia coli depends upon a system which is determined by at least two genetic loci. Mutants which carry a deletion of the tonB-trp region of the chromosome grow only when very high concentrations of iron are present in the medium. These strains are sensitive to chromic ion (Cr(3+)) and, unlike the parent strain, fail to grow on MnSO(4) when FeSO(4) is not added to the medium. A second type of mutant, Chr2, which was isolated on the basis of its sensitivity to chromic ion, also requires a high concentration of iron for growth. This mutant can be distinguished phenotypically from the deletion mutants since it grows normally on low concentrations of iron, provided citrate is added to the medium. The chromium sensitivity of both types of mutants can be reversed by high concentrations of exogenous iron. The data are interpreted to indicate that the E. coli mutants studied are defective in iron transport and that residual iron transport is in some way inhibited by chromic ion.

Iron transport in Escherichia coli: roles of energy-dependent uptake and 2,3-dihydroxybenzoylserine

Escherichia coli strains B/r and 2276 contain an active transport system for iron. The system is energy-dependent, repressed by excess iron in the growth medium, and capable of accumulating iron inside of the cells at concentrations 2,000-fold higher than those in the medium. Two tonB-trp deletion mutants, strains B/rlt and B/lt7, which are sensitive to chromic ion and require high levels of iron for normal growth, are deficient in this active transport system. A point mutant, strain Chr2, which is also sensitive to chromic ion and requires high levels of iron for growth, has the active uptake system but cannot synthesize a specific chelator for iron, 2,3-dihydroxybenzoylserine (DHBS). Evidence is presented to support the hypothesis that both the active uptake system and chelation of iron by DHBS play a role in iron uptake from iron-deficient medium. The chromium sensitivity of the mutants can be explained by inhibition of uptake of exogenous iron.

Hemoglobin variant common to Chinese and North American Indians: alpha-2-beta-22 Glu-Ala

An electrophoretically slow hemoglobin variant, in which the structural change involves the replacement of a glutamyl residue by alanyl at position beta-22, was reported in two groups of North American Indians: hemoglobin-G Coushatta, in Alabama-Coushatta Indians in Texas; and hemoglobin-G Saskatoon, in descendants of Santee Indians living in Canada. Hemoglobin-G Hsin-Chu, found in Taiwan in a Chinese from the northern Chinese province of Liaoning, is now shown to have the same structural anomaly.

Nonlinear optics

Recent advances in the field of nonlinear optical phenomena are reviewed with particular emphasis placed on such topics as parametric oscillation, self-focusing and trapping of laser beams, and stimulated Raman, Rayleigh, and Brillouin scattering. The optical frequency radiation is treated classically in terms of the amplitudes and phases of the electromagnetic fields. The interactions of light waves in a material are then formulated in terms of Maxwell's equations and the electric dipole approximation. In this method, non-linear susceptibility tensors are introduced which relate the induced dipole moment to a power series expansion in field strengths. The tensor nature and the frequency dependence of the nonlinearity coefficients are considered. The various experimental observations are described and interpreted in terms of this formalism.

The Earliest Stages of Development of the Blood-vessels and of the Heart in Ferret Embryos

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The Earliest Stages of Development of the Blood-vessels and of the Heart in Ferret Embryos

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