Ultraviolet light

About: Ultraviolet light is a research topic. Over the lifetime, 49494 publications have been published within this topic receiving 843151 citations.

Seasonal dynamics of colored dissolved material in the Sargasso Sea

Abstract: Observations from the Sargasso Sea have shown that the light attenuation spectrum is a function of both phytoplankton pigments and a detrital-like component that varies independently. Here we examine the nature and dynamics of these detrital-like variations by analyzing a time-depth series of visible and ultraviolet light absorption spectra for colored (chromophoric) dissolved materials [CDOM; ag(λ)] and detrital particulates [ad(λ)] collected at the US JGOFS Bermuda Atlantic time-series study (BATS) site. At 440 nm, CDOM absorption, ag(440), made up of on an average more than one-half of the total non-water absorption coefficient, while detrital particulate absorption, ad(440), was generally a minor constituent. The vertically integrated stock of CDOM (0–140 m) increased from the beginning of spring until the end of summer in 1994 and 1995, although near-surface values (⩽40 m) were strongly depressed near the surface at the peak of summer. This summertime reduction of the mixed layer ag(λ) is likely due to photooxidation of CDOM to optically inactive forms. Further, values of CDOM absorption were unrelated directly to indices of total water column dissolved organic carbon (DOC) stocks measured at BATS. We hypothesize that CDOM is produced as a by-product of the microbial breakdown of DOC and is destroyed due to photooxidation. Summertime CDOM dynamics at this site can be quantified with these two processes, as mixing below the summertime mixed layer can be assumed to be small. Our results imply, for the first time in the blue ocean, a link between microbial community activity and CDOM dynamics and clearly provide an explanation for the nature of non-chlorophyll light attenuation observed in the Sargasso Sea.

A yeast strain for simultaneous detection of induced mitotic crossing over, mitotic gene conversion and reverse mutation

Abstract: A diploid yeast strain is described which can be used to study induction of mitotic crossing over, mitotic gene conversion and reverse mutation. Mitotic crossing over can be detected visually as pink and red twin sectored colonies which are due to the formation of homozygous cells of the genotype ade240/ade240 (deep red) and ade-2-119/ade2-119 (pink) from the originally heteroallelic condition ade2-40/ade2-119 which forms white colonies. Mitotic gene conversion is monitored by the appearance of tryptophan non-requiring colonies on selective media. The alleles involved are tryp5-12 and trp5-27 derived from the widely used strain D4. Mutation induction can be followed by the appearance of isoleucine non-requiring colonies on selective media. D7 is homoallelic ilv1-92/ilv1-92 . The isoleucine requirement caused by ilv1-92 can be alleviated by true reverse mutation and allele non-specific suppressor mutation. The effects of ethyl methanesulfonate (EMS), nitrous acid, ultraviolet light and hycanthone methanesulfonate were studied with D7 stationary phase cells. Mitotic crossing over as monitored by red/pink twin sectored colonies was almost equally frequent among normal and convertant cells. This showed again that mitotic recombination is not due to the presence fo a few cells committed to meiosis in an otherwise mitotic cell population. The dose-response curves for induction of mitotic gene conversion and reversion of the isoleucine requirement were exponential. In contrast to this, the dose-response curve for induction of twin sectored red and pink colonies reached a plateau at doses giving about 30% cell killing. This could partly be due to lethal segregation in the progeny of treated cells. None of the agents tested would induce only one type of mitotic recombination, gene conversion or crossing over. There was, however, some mutagen specificity in the induction of isoleucine prototrophs.

Guidelines of Care for the Management of Psoriasis and Psoriatic Arthritis. Section 3. Guidelines of Care for the Management and Treatment of Psoriasis With Topical Therapies

Abstract: Psoriasis is a common, chronic, inflammatory, multi-system disease with predominantly skin and joint manifestations affecting approximately 2% of the population. In this third of 6 sections of the guidelines of care for psoriasis, we discuss the use of topical medications for the treatment of psoriasis. The majority of patients with psoriasis have limited disease (<5% body surface area involvement) and can be treated with topical agents, which generally provide a high efficacy-to-safety ratio. Topical agents may also be used adjunctively for patients with more extensive psoriasis undergoing therapy with either ultraviolet light, systemic or biologic medications. However, the use of topical agents as monotherapy in the setting of extensive disease or in the setting of limited, but recalcitrant, disease is not routinely recommended. Treatment should be tailored to meet individual patients' needs. We will discuss the efficacy and safety of as well as offer recommendations for the use of topical corticosteroids, vitamin D analogues, tazarotene, tacrolimus, pimecrolimus, emollients, salicylic acid, anthralin, coal tar, as well as combination therapy.

Cis-trans isomers of vitamin a and retinene in the rhodopsin system

Abstract: Vitamin A and retinene, the carotenoid precursors of rhodopsin, occur in a variety of molecular shapes, cis-trans isomers of one another. For the synthesis of rhodopsin a specific cis isomer of vitamin A is needed. Ordinary crystalline vitamin A, as also the commercial synthetic product, both primarily all-trans, are ineffective. The main site of isomer specificity is the coupling of retinene with opsin. It is this reaction that requires a specific cis isomer of retinene. The oxidation of vitamin A to retinene by the alcohol dehydrogenase-cozymase system displays only a low degree of isomer specificity. Five isomers of retinene have been isolated in crystalline condition: all-trans; three apparently mono-cis forms, neoretinenes a and b and isoretinene a ; and one apparently di-cis isomer, isoretinene b . Neoretinenes a and b were first isolated in our laboratory, and isoretinenes a and b in the Organic Research Laboratory of Distillation Products Industries. Each of these substances is converted to an equilibrium mixture of stereoisomers on simple exposure to light. For this reaction, light is required which retinene can absorb; i.e ., blue, violet, or ultraviolet light. Yellow, orange, or red light has little effect. The single geometrical isomers of retinene must therefore be protected from low wave length radiation if their isomerization is to be avoided. By incubation with opsin in the dark, the capacity of each of the retinene isomers to synthesize rhodopsin was examined. All-trans retinene and neoretinene a are inactive. Neoretinene b yields rhodopsin indistinguishable from that extracted from the dark-adapted retina (λmax· 500 mµ). Isoretinene a yields a similar light-sensitive pigment, isorhodopsin , the absorption spectrum of which is displaced toward shorter wave lengths (λmax· 487 mµ). Isoretinene b appears to be inactive, but isomerizes preferentially to isoretinene a , which in the presence of opsin is removed to form isorhodopsin before the isomerization can go further. The synthesis of rhodopsin in solution follows the course of a bimolecular reaction, as though one molecule of neoretinene b combines with one of opsin. The synthesis of isorhodopsin displays similar kinetics. The bleaching of rhodopsin, whether by chemical means or by exposure to yellow or orange ( i.e ., non-isomerizing) light, yields primarily or exclusively all-trans retinene. The same appears to be true of isorhodopsin. The process of bleaching is therefore intrinsically irreversible. The all-trans retinene which results must be isomerized to active configurations before rhodopsin or isorhodopsin can be regenerated. A cycle of isomerization is therefore an integral part of the rhodopsin system. The all-trans retinene which emerges from the bleaching of rhodopsin must be isomerized to neoretinene b before it can go back; or if first reduced to all-trans vitamin A, this must be isomerized to neovitamin A b before it can regenerate rhodopsin. The retina obtains new supplies of the neo- b isomer: ( a ) by the isomerization of all-trans retinene in the eye by blue or violet light; ( b ) by exchanging all-trans vitamin A for new neovitamin A b from the blood circulation; and ( c ) the eye tissues may contain enzymes which catalyze the isomerization of retinene and vitamin A in situ . When the all-trans retinene which results from bleaching rhodopsin in orange or yellow light is exposed to blue or violet light, its isomerization is accompanied by a fall in extinction and a shift of absorption spectrum about 5 mµ toward shorter wave lengths. This is a second photochemical step in the bleaching of rhodopsin. It converts the inactive, all-trans isomer of retinene into a mixture of isomers, from which mixtures of rhodopsin and isorhodopsin can be regenerated. Isorhodopsin, however, is an artefact. There is no evidence that it occurs in the retina; nor has isovitamin A a or b yet been identified in vivo . In rhodopsin and isorhodopsin, the prosthetic groups appear to retain the cis configurations characteristic of their retinene precursors. In accord with this view, the s-bands in the absorption spectra of both pigments appear to be cis peaks. The conversion to the all-trans configuration occurs during the process of bleaching. The possibility is discussed that rhodopsin may represent a halochromic complex of a retinyl ion with opsin. The increased resonance associated with the ionic state of retinene might then be responsible both for the color of rhodopsin and for the tendency of retinene to assume the all-trans configuration on its release from the complex. A distinction must be made between the immediate precursor of rhodopsin, neovitamin A b , and the vitamin A which must be fed in order that rhodopsin be synthesized in vivo . Since vitamin A isomerizes in the body, it is probable that any geometrical isomer can fulfill all the nutritional needs for this vitamin.