component (t = 4.7 ns). This rvalue is consistent with previous (room temperature) estimates of donor-acceptor center to center distance of 25 A. The most important result is that the simplified kinetics at room temperature argue that any structural states of the complex which arc trapped at 77 K are largely equilibrated at 300 K within 5 ns. This result suggests that motion at the cytc/ccp interface can be quite rapid and offers experimental support for the rapid restricted dimensional diffusion model of the eyie-eep complex suggested by Brownian dynamics.8 With this information now available, more detailed insight into the nature of the binding sites in principle could be obtained by comparing the decay distributions for the native systems with those for site-specific mutants.9'10 Such studies are in progress.

The synthesis of palmitate, stearate, and cholesterol in liver and nervous tissues (brain, cord, and nerve) of Sprague-Dawley rats was determined using deuterated water (D2O) and mass isotopomer analysis. Rats were given 4% deuterium in their drinking water after each receiving an intraperitoneal priming dose. Animals were killed at 1, 2, 4, and 8 wk for deuterium enrichment in body water and determination of mass isotopomer distribution in lipids from various tissues. In 1 wk, the enrichment in the body water reached a plateau of 2.6%, which is 65% of that in the drinking water. We observed the maximum incorporation number (N) in all lipids to be higher than those previously observed, being 22, 24, and 30 for liver palmitate, stearate, and cholesterol, respectively, and N may vary among tissues. Using a single exponential model, we found the half-time (t1/2) and the plateau levels of the newly synthesized lipids of the nervous tissues (t1/2 values ranging from 5 to 28 days) to be different from those of the liver (t1/2 values < or = 4 days) in this relatively long-term study. Mass isotopomer distribution analysis and D2O can be used not only to quantitate the replacement rate of many lipids in various compartments but may also be used to elucidate the tissue-specific synthetic pathways from N.

We report δD and δ13C measurements of atmospheric CH4 from air samples collected from two locations in the United States. They are the mid continental site Niwot Ridge, Colorado (40°N, 105°W), and a Pacific coastal site receiving strong westerlies, Montaña de Oro, California (35°N, 121°W). Data from multiyear approximately bimonthly sampling provide information relating seasonal cycling of CH4 sources and sinks in background air, record long‐term trends in CH4 mixing and isotope ratio related to the atmospheric CH4 loading, and may indicate regional CH4 sources. At Niwot Ridge, δD‐CH4 averaged −93.1 ± 3.0‰ from 1999 to 2001, while δ13C‐CH4 averaged −47.22 ± 0.13‰ from 1995 to 2001 with distinct seasonal cycles in both isotope ratios. At Montaña de Oro, atmospheric CH4 was observed to be more depleted in 13C and D: Measured δD‐CH4 averaged −97.3 ± 3.7‰ from 2000 to 2001, while δ13C‐CH4 averaged −47.26 ± 0.17‰ from 1996 to 2001, and seasonal cycles were larger than those observed at Niwot Ridge. Mixing ratios observed at Montaña de Oro were higher on average than at Niwot Ridge. At both sites, δ13C‐CH4 was found to correlate poorly with mixing ratio, an indication that varying CH4 sources are partly responsible for the δ13C‐CH4 seasonal signal. In contrast, a strong anticorrelation exists between δD‐CH4 and mixing ratio, with maxima and minima approximately 6 months out of phase, indicating a sensitivity of δD to sink processes. The dual isotopic constraint to atmospheric CH4 seasonality implies that these midlatitude sites are annually influenced by a 13C‐enriched CH4 source(s) seasonally increasing in late spring and a 13C‐depleted CH4 source(s) seasonally increasing in late summer or early fall.

Objectives: American female adolescents are at high risk of a physically inactiveHfestyle that likely leads to health problems later in life. We hypothesized that a brief program of endurance exercise training in female adolescents would result in increased energy expenditure and quantifiable structural and functional adaptations.Siudy design: Forty-four high school girls (aged 15 to 17 years, none were elite aJ,hletes) enrolled in a 5-day per week anatomy class for 5 weeks and were randomly assigned to control (n = 22) and training groups. All subjects participated in a 2-hour daily teaching program. During the remaining time (2 hours), the trainUng group members underwent endurance-type training and control group subjects participated in a computer workshop. The intervention was assessed by (I) comparison of total energy expenditure between groups with the doubly labeled water technique, (2) determination of changes in thigh muscle volume by magnetic resonance imaging, and (3) determination of changes in maximal oxygen uptake by use of respiratory gas exchange responses.Results: Total energy expenditure was significantly greater (15.3%) in the training group compared with the control subjects (p <0.003). Five weeks of training led to a 4.3% ± I% increase in thigh muscle volume (p <0.0002) and a 12.1% ± 3.7% increase in maximal oxygen uptake (p <0.004); there were no changes in the control group. The training effect was most pronounced in the least fit subjects.Conclusions: Exercise training programs for female adolescents can be successfully integrated into a high school summer curriculum. Quantifiable, substantial structural and functional responses occur with relatively short periods of training. Approximately 60% of the training response was related to factors independent of muscle size per se. These data may serve to better design physical activity programs for female adolescents.

increasing temperature over the range studied. These results agree well with experimental studies using tunable diode laser absorption spectroscopy and FTIR absorption spectroscopy and with a recent theoretically-calculated set of values.