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M Calvin

Publications and source records attributed to M Calvin.

82 records · Page 5Linked to original sources
PubMed1967

Thermodynamics of light emission and free-energy storage in photosynthesis.

A Planck law relationship between absorption and emission spectra is used to compute the fluorescence spectra of some photosynthetic systems from their absorption spectra. Calculated luminescence spectra of purple bacteria agree well but not perfectly with published experimental spectra. Application of the Planck law relation to published activation spectra for Systems I and II of spinach chloroplasts permits independent calculation of the luminescence spectra of the two systems; if the luminescence yield of System I is taken to be one-third the yield of System II, then the combined luminescence spectrum closely fits published experimental measurement.Consideration of the entropy associated with the excited state of the absorbing molecules is used to compute the oxidation-reduction potentials and maximum free-energy storage resulting from light absorption. Spinach chloroplasts under an illumination of 1 klux of white light can produce at most a potential difference of 1.32 ev for System I, and 1.36 ev for System II. In the absence of nonradiative losses, the maximum amount of free energy stored is 1.19 ev and 1.23 ev per photon absorbed for Systems I and II, respectively. The bacterium Chromatium under an illumination of 1 mw/cm(2) of Na D radiation can produce at most a potential difference of 0.90 ev; the maximum amount of free energy stored is 0.79 ev per photon absorbed.The combined effect of partial thermodynamic reversibility and a finite trapping rate on the amount of luminescence is considered briefly.

Chloroplasts↗
PubMed1966

Thymine addition to ethanol: induction by gamma irradiation.

When thymine in dilute, deaerated, aqueous solution was irradiated with gamma-rays in the presence of ethanol, a high yield of products containing both the thymine and ethanol moieties was obtained. These were shown to be isomers formed by the attack of CH(3)CHOH radicals at the carbon No. 6 position of thymine. A similar reaction was observed with N, N'-dimethylthymine, but O,O'-dimethylthymine did not react. The reaction may be relevant to the resistance of certain cells to ionizing radiation.

Chemical Phenomena↗
PubMed1965

Lifetime of bacterial messenger ribonucleic acid.

Moses, V. (University of California, Berkeley), and M. Calvin. Lifetime of bacterial messenger ribonucleic acid. J. Bacteriol. 90:1205-1217. 1965.-When cells from a stationary culture of Escherichia coli were placed in fresh medium containing inducer for beta-galactosidase, growth, as represented by increase in turbidity and by total protein synthesis, started within 30 sec. By contrast, beta-galactosidase synthesis was greatly delayed compared with induction during exponential growth. Two other inducible enzymes (d-serine deaminase and l-tryptophanase) and one repressible enzyme (alkaline phosphatase) showed similar lags. The lags were not due to catabolite repression. They could not be reduced by pretreatment of the culture with inducer, or by supplementing the fresh medium with amino acids or nucleotides. The lag was also demonstrated by an i(-) mutant constitutive for beta-galactosidase synthesis. An inhibitor of ribonucleic acid (RNA) synthesis, 6-azauracil, preferentially inhibited beta-galactosidase synthesis compared with growth in both inducible and constitutive strains. Puromycin, an inhibitor of protein synthesis, acted as an inhibitor at additional sites during the induction of beta-galactosidase synthesis. No inhibition of the reactions proceeding during the first 20 sec of induction was observed, but puromycin seemed to prevent the accumulation of messenger RNA during the period between 20 sec and the first appearance of enzyme activity after 3 min. It is suggested that these observations, together with many reports in the literature that inducible enzyme synthesis is more sensitive than total growth to some inhibitors and adverse growth conditions, can be explained by supposing that messenger RNA for normally inducible enzymes is biologically more labile than that for some normally constitutive proteins. The possible implications of this hypothesis for the achievement of cell differentiation by genetic regulation of enzyme synthesis are briefly discussed.

Chemical Phenomena↗
PubMedDate not supplied

Chemical evolution.

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Biochemical Phenomena↗