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ABSTRACT: Abstract— –When washed cells of histidine-grown Pseudomonas putida were incubated at 8°C in darkness, urocanase activity diminished after several days; most of this lost activity could be restored by treatment of cell extracts with near-u.v. light. Sunlight and daylight were also effective for activation. Non-irradiated extract, when added to the active preparation, did not inhibit the enzyme activity. Heated and boiled extracts with or without irradiation did not catalyze the urocanase reaction nor did they change the activity of an activated extract when added to it. Photoactivation of cell extracts did not require oxygen, was not dependent on temperature and was not prevented by dialysis. Urocanase purified by gel electrophoresis was capable of light activation. It is suggested that the photoreceptor is closely associated with urocanase since it is not separated from the enzyme by dialysis or electrophoresis.
Photochemistry and Photobiology 01/2008; 13(2):171 - 177. · 2.41 Impact Factor
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ABSTRACT: We study the propagation of orientation waves in a director field with rotational inertia and potential energy given by the Oseen-Frank energy functional from the continuum theory of nematic liquid crystals. There are two types of waves, which we call splay and twist waves. Weakly nonlinear splay waves are described by the quadratically nonlinear Hunter-Saxton equation. Here, we show that weakly nonlinear twist waves are described by a new cubically nonlinear, completely integrable asymptotic equation. This equation provides a surprising representation of the Hunter-Saxton equation as an advection equation. There is an analogous representation of the Camassa-Holm equation. We use the asymptotic equation to analyze a one-dimensional initial value problem for the director-field equations with twist-wave initial data.
10/2006;
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ABSTRACT: We derive an asymptotic solution of the vacuum Einstein equations that describes the propagation and diffraction of a localized, large-amplitude, rapidly-varying gravitational wave. We compare and contrast the resulting theory of strongly nonlinear geometrical optics for the Einstein equations with nonlinear geometrical optics theories for variational wave equations.
12/2005;
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Aviation Space and Environmental Medicine 03/2003; 74(2):187; author reply 188. · 0.88 Impact Factor
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SIAM Journal of Applied Mathematics. 01/2000; 61:131-148.
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ABSTRACT: Urocanase activity in Pseudomonas putida cells showed periodic changes corresponding to a light-dark cycle. Apparent interconversion of the active and inactive forms of urocanase was accomplished by photoactivation by nearultraviolet light and by dark thermal inactivation. The purified enzyme exhibited similar behavior. This system suggests a possible molecular basis for an hour-glass timer. Photoinactivation by light of 290 nm alternated with photoactivation at 340 nm also generated regular changes in urocanase activity.
Archives of Microbiology 02/1972; 86(1):83-90. · 1.43 Impact Factor
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ABSTRACT: We use the method of characteristics to prove the short-time existence of smooth solutions of the unsteady inviscid Prandtl equations, and present a simple explicit solution that forms a singularity in finite time. We give numerical and asymptotic solutions which indicate that this singularity persists for nonmonotone solutions of the viscous Prandtl equations. We also solve the linearization of the inviscid Prandtl equation about shear flow. We show that the resulting problem is weakly, but not strongly, well-posed, and that it has an unstable continuous spectrum when the shear flow has a critical point, in contrast with the behavior of the linearized Euler equations.
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ABSTRACT: The photomodulation of enzymes involves the activation and inactivation of enzyme reactions by UV and visible light. Enzymes or their reactions may be affected directly or indirectly. Direct effects involve photoproduction of a substrate, photodissociation of an inhibitor, photochemistry of protein amino acids, irradiation of a chromophore and irradiation of an enzyme substrate. Indirect effects involve gene expression, phytochrome and other photoreceptors which are not part of the enzyme, protein synthesis, membranes and photosynthesis. Photoactivation of enzymes is related to photocarcinogenesis, photomorphogenesis of plants, primary effects or side effects of phototherapy, deoxyribose nucleic acid (DNA) repair and many other aspects of biology and medicine. Model systems may contribute to the knowledge of protein chemistry and medicinal chemistry.
Journal of Photochemistry and Photobiology B: Biology.
