The thermal decomposition of visual purple

Lythgoe, R. J.; Quilliam, J. P.

doi:10.1113/jphysiol.1938.sp003622

Cited by 60 publications

(28 citation statements)

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“…The effect of temperature on the thermal bleaching of rhodopsin has been described by Lythgoe and Quilliam (1938; cf. their Fig.…”

Section: N___b ----E_~lnr ' Nmentioning

confidence: 99%

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The Interplay of Light and Heat in Bleaching Rhodopsin

George

1952

Journal of General Physiology

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I mTRODVCTIONThe absorption of light by rhodopsin in the retina activates the pigment molecules and leads eventually to the stimulation of rod vision. The initial light reaction is followed by a sequence of thermal reactions occurring equally in light or darkness, by which the rhodopsin, a conjugated carotenoid protein, ultimately bleaches to retinenel and protein (Wald, Durell, and St. George, 1950). The work described here deals with the initial activation of rhodopsin.Rhodopsin can be bleached not only by light but by heat. At 50°C. or above it bleaches rapidly in the dark and at a rate that is very temperature-dependent. Lythgoe and Quilliam (1938) calculated an experimental activation energy of 44 kg. cal. per mole from their data on the temperature coefficient in neutral solutions. On the other hand, the rate of bleaching by white light is not temperature-dependent, showing that no thermal activation is needed (Hecht, 1920-21).The purpose of the following research was to study the transition between photic and thermal activation. The argument runs as follows. On going from shorter wave lengths to red light a point should be reached beyond which the incident quanta cannot supply the entire energy needed to activate the rhodopsin molecule. If bleaching is to occur nonetheless, the deficit will have to be met by a contribution of thermal energy from the internal degrees of freedom of the molecule. There should therefore be a critical wave length beyond which the bleaching by light becomes temperature-dependent.Measurement of the temperature coefficient of bleaching at intervals along the wave length scale showed that a temperature dependence does in fact appear in the orange at about 590 mu. Moreover, the quantum energy at this wave length differs very little from the activation energy observed in heat bleaching. At wave lengths longer than 590 mt~, the temperature coefficient increases regularly so that the sum of the energy of the absorbed quanta and the thermal ac-

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“…The effect of temperature on the thermal bleaching of rhodopsin has been described by Lythgoe and Quilliam (1938; cf. their Fig.…”

Section: N___b ----E_~lnr ' Nmentioning

confidence: 99%

“…or above it bleaches rapidly in the dark and at a rate that is very temperature-dependent. Lythgoe and Quilliam (1938) calculated an experimental activation energy of 44 kg. cal.…”

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The Interplay of Light and Heat in Bleaching Rhodopsin

George

1952

Journal of General Physiology

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“…Recent investigations by Lythgoe and Quilliam (1938) suggest th a t visual purple is bleached by interaction with the solvent water molecules. If this is the case it is easy to see how a quantum efficiency of unity might arise-the visual purple chromophore grouping is presumably surrounded by water molecules with which it may react when it has absorbed a light quantum.…”

Section: Discussionmentioning

confidence: 99%

“…5 a, 56) for which R. temp were used. The solutions were buffered to a pH of 9-3 and were maintained a t constant temperature in the range between 19 and 27° C, where the thermal decomposition was negligible (Lythgoe and Quilliam 1938). The cells used for the experiments had areas, as follows: nos.…”

Section: R Esultsmentioning

confidence: 99%

The spectral variation of the photosensitivity of visual purple

Schneider

Goodeve

Lythgoe

1939

Proc. R. Soc. Lond. A

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1. I n tr o d u ctio n I t is generally accepted that, in scotopic vision, the first stage in the con version of the electromagnetic wave into a nerve impulse involves the photo chemical bleaching of visual purple. Whilst the quantitative relation between visual purple and scotopic vision has been recognized for many years (Konig 1894), it is only recently th a t this relation has been more accurately expressed (Hecht and Williams 1922; D artnall and Goodeve 1937).Quantitative measurements of the photochemical bleaching of visual purple have recently been described (Dartnall, Goodeve andLythgoe 1936 and; to be referred to as " the previous papers"). A new photochemical method, " the method of photometric curves ", was used leading to a general equation for the rate of bleaching by monochromatic light. This rate is governed by the " photosensitivity" , which is the product of the extinction coefficient and the quantum efficiency. In the case of visual purple the quantum efficiency is defined as the number of chromophoric groupings decomposed per quantum absorbed. In the previous papers the photo sensitivity was measured at a wave-length corresponding to the maximum of the absorption and it was found to be independent of pH. and temperature and to have an absolute value of 9 x 10-17cm.2 Reasons for thinking th a t the quantum efficiency is about unity were given (see § 5 below). In order to get further information about the photochemical mechanism of the bleach ing process and its relation to scotopic vision, these measurements have now been extended to other wave-lengths. The results for the visible region are described below, while those for the ultra-violet will be described in a later paper. * 2. T h e method of ph otom etric curves A parallel beam of monochromatic light is passed through a small cylindrical cell with parallel faces containing the solution to be investigated [ 102 ] on May 12, 2018 http://rspa.royalsocietypublishing.org/ Downloaded from

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“…Hosoya (8) described "Nachbleichung" first and it was confirmed by Wald (9) and Lythgoe (4). And Lythgoe (4,10) reported that the indicator yellow solution was unstable at pH6.5-3.5 and decomposed thermally at this pH range especially at pH5.2. The exhibition of a deeper yellow color in the retina TH2 at the final stadium of bleaching which I observed, occurred at this range of pH only.…”

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The Influence of Hepatectomy With Ligation of the Posterior Vena Cava on the Bleaching of Visual Purple and the Thermal Decomposition of Indicator Yellow

Peng

1950

Jpn.J.Physiol

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The thermal decomposition of visual purple

Cited by 60 publications

References 6 publications

The Interplay of Light and Heat in Bleaching Rhodopsin

The Interplay of Light and Heat in Bleaching Rhodopsin

The spectral variation of the photosensitivity of visual purple

The Influence of Hepatectomy With Ligation of the Posterior Vena Cava on the Bleaching of Visual Purple and the Thermal Decomposition of Indicator Yellow

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