Showing papers by "Rienk van Grondelle published in 1994"

The Primary Steps of Photosynthesis

Abstract: Photosynthesis, the process by which plants convert solar energy into chemical energy, results in about 10 billion tons of carbon entering the biosphere annually as carbohydrate—equivalent to about eight times mankind's energy consumption in 1990. The apparatus used by plants to perform this conversion is both complex and highly efficient. Two initial steps of photosynthesis—energy transfer and electron transfer—are essential to its efficiency: Molecules of the light‐harvesting system transfer electronic excitation energy to special chlorophyll molecules, whose role is to initiate the directional transfer of electrons across a biological membrane; the electron transfer, which takes place in a pigment‐protein complex called the reaction center, then creates a potential difference that drives the subsequent biochemical reactions that store the energy. (Higher plants use two different reaction centers, called photosystems I and II, while purple bacteria make do with a single reaction center. The difference i...

POLARIZED SITE‐SELECTION SPECTROSCOPY OF CHLOROPHYLL a IN DETERGENT

Abstract: Monomeric chlorophyll a (Chl a) was obtained from the isolated core antenna complex CP47 of photo-system II after incubation with the detergent triton X-100 and was studied by low-temperature polarized light spectroscopy with the aim to obtain model spectra for Chi a in intact photosynthetic complexes. Evidence is presented by circular dichroism and anisotropy measurements that the isolated chlorophyll is monomeric. The absorption bandwidths are relatively large compared to those found in photosynthetic complexes due to inhomogeneous broadening introduced by the detergent. By selective laser excitation at low temperature, considerable narrowing can be achieved. A number of vibrational bands are resolved in the site-selected, polarized absorption and fluorescence emission spectra. The emission spectrum of Chi a in detergent-damaged CP47 is compared with that of Chi a in the intact light-harvesting complex of photosystem II (LHC-II) from green plants. The spectra are remarkably similar indicating that the low-temperature thermal emitter in LHC-II has spectral properties that are very similar to those of monomeric Chl a.