PHOTOSYNTHESIS:
New Primary Reactions
NASA's Paine Doing something about time
When it was hot, these metals could have vaporized. Some confirmation for this view of a hot period came from findings of Dr. Mitsunobu Tatsumoto and Dr. John N. Rosholt of the U.S. Geological Survey. They report that most of the lead—also a volatile metal—in the lunar samples came from the decay of uranium and little if any from other sources. This finding indicates that any lead present when the moon formed may since have vaporized and thus disappeared from the lunar environment. The isotopic study of lead, thorium, and uranium in the samples gives an estimate of the age of lunar dust and breccia of 4.6 billion years, Dr. Tatsumoto says. But crystalline rocks appear to be 1 billion years younger. No full explanation for the difference exists. The approximate age of crystalline material from the Sea of Tranquillity at 3.6 billion years is also the estimate of Dr. G. J. Wasserburg and associates at California Institute of Technology. His group's studies of the age of rocks from the lunar surface and of effects of cosmic radiation on them indicate that lava flowed at this time, about 1 billion years after the moon formed. Their studies imply the moon formed along with the rest of the planets. Dr. Wasserburg's work so far also suggests that the exterior of the moon melted to a depth of 100 or more kilometers 3.6 billion years ago because of impact or internal heat. If the heat came from impact, it also is likely that the earth received a heavy bombardment at the same time. This may be the reason why there is no geologic record of the earth before roughly 3.6 billion years. 12 C&EN JAN. 12, 1970
The mechanism of photosynthesis has come into sharper focus with the discovery of two new reaction steps that until now have gone undetected. One involves the photooxidation of cytochrome brifVi„ a component of chloroplasts. The other concerns the photoreduction of a newly found constituent of chloroplasts, C550, for which there is only spectral evidence. Both reactions are basic to the primary, light-actuated events in photosyn diesis, note the codiscoverers, cell physiologists David B. Knaft and Daniel I. Anion, University of California, Berkeley. Supporting such a conclusion is the fact that the reactions proceed even at the temperature of liquid nitrogen. This is the first instance to date of a low-temperature photooxidation of a b-type cytochrome and of any kind of lowtemperature photoreduction in chloroplasts, the Berkeley biochemists contend. These reactions play key roles in the mechanism of System II of photosynthesis. This system involves the extraction of electrons from water and their transferal to ferredoxin. In the first light-driven step, C550 captures the extracted electrons and then passes them on to cytochrome t>55i» °y w a y °f a series of light-independent, "dark" steps. In the second light-driven step, the reduced cytochrome br)r>
