Fluorescence lifetimes of dimers and higher oligomers of bacteriochlorophyll c from Chlorobium limicola

Fluorescence lifetimes have been measured for bacteriochlorophyll (BChl) c isolated from Chlorobium limicola in different states of aggregation in non-polar solvents. Two different homologs of BChl c were used, one with an isobutyl group at the 4 position, the other with n-propyl. Species previously identified as dimers (Olson and Pedersen 1990, Photosynth Res, this issue) decayed with lifetimes of 0.64 ns for the isobutyl homolog, 0.71 ns for n-propyl. Decay-associated spectra indicate that the absorption spectrum of the isobutyl dimer is slightly red-shifted from that of the n-propyl dimer. Aggregates absorbing maximally at 710 nm fluoresced with a principal lifetime of 3.1 ns, independent of the homolog used. In CCl₄, only the isobutyl homolog forms a 747-nm absorbing oligomer spectrally similar to BChl c in vivo. This oligomer shows non-exponential fluorescence decay with lifetimes of 67 and 19 ps. Because the two components show different excitation spectra, the higher oligomer is probably a mixture of more than one species, both of which absorb at 747 nm.Abbreviations BChl bacteriochlorophyll - Chl chlorophyll - % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGGipm0dc9vqaqpepu0xbbG8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Xdm2aaW% baaSqabeaacaaIYaaaaaaa!3777!\[\chi ^2 \] chi-square - FWHM full-width at half-maximum     

Demography of agile gibbons (Hylobates agilis)

Demographic processes and the structure of a population of agile gibbons (Hylobates agilis) were investigated over 6 years in the Gunung Palung Reserve, Indonesia. Estimates of population size, density, and biomass revealed a population whose groups were stable in size and composition. Demographic processes place gibbons at risk, however, to short-term changes in their environment. Patterns of survival, fecundity, mortality, and dispersal combined to produce negative rates of growth. In addition, a top-heavy age-class distribution, with adults forming a large fraction of animals, makes it unlikely that this population could recover rapidly from a decline in numbers. Two behavioral factors, territoriality and monogamy, account for the size and stability of gibbon groups. Monogamy imposes limits on group size, while mating patterns and territoriality decrease the impact of sources of high mortality common in other primate species. These relationships underscore the fundamental importance of behavioral influence on demographic processes and social structure.     

Oxygen consumption and body temperature in yellow-bellied marmot populations from montane-mesic and lowland-xeric environments

Summary Yellow-bellied marmots characteristically live in montane-mesic environments, but in several areas in western North America, this species extended its range into lowland-xeric habitats. Body mass was significantly smaller in the lowland-xeric population from eastern Washington at 393 m than in the montane-mesic population from western Colorado at 2900 m. Oxygen consumption of marmots from montane-mesic and lowland-xeric environments was signiflcantly affected by ambient temperature (T_A) water regimen, population, and a population x water regimen x temperature interaction. Lowland-xeric animals had a higher metabolic rate at low T_As, but a lower metabolic rate at higher T_As than the montane-mesic aminals. Oxygen consumption was lower on a restricted-water regimen than on ad libitum water in both populations. Coefficients relating oxygen consumption to body mass were affected by T_A, water regimen, and population. These intraspecific coefficients are larger than the interspecific coefficients for all mammals. Body temperature (T_B) was affected significantly by T_A, water regimen, and population. T_A body mass, and a population x water regimen interaction significantly affected conductance. Conductance generally was higher in the lowland-xeric than in the montane-mesic marmots. Both populations increased conductance at high T_A, but the lowland-xeric population dissipated a much higher proportion of the heat by evaporative water loss (EWL) than did the montane-mesic population. Metabolic water production exceeded or equaled EWL at 5–20°C. Smaller body size, reduced metabolism at high T_A, and increased EWL at high T_A characterized the lowland-xeric population.Metabolic rates of yellow-bellied marmots were higher than predicted from body size during the reproductive season but decreased to 67% of that predicted from the Kleiber curve by late summer. Marmots minimize thermoregulatory costs by concentrating activity at times when the microclimate is favorable, by tolerating hyperthermia at high T_A in the field, and by having a conductance lower than that predicted from body size.Abbreviations DHC dry-heat conductance - EHL evaporative heat loss - EWL evaporative water loss - HP heat produced - T _A ambient temperature - T _n body temperature - M body mass     

Assessment of methods to determine minimal cellulase concentrations for efficient hydrolysis of cellulose

Summary The enzyme loading needed to achieve substrate saturation appeared to be the most economical enzyme concentration to use for hydrolysis, based on percentage hydrolysis. Saturation was reached at 25 filter paper units per gram substrate on Solka Floc BW300, as determined by studying (a) initial adsorption of the cellulase preparation onto the substrate, (b) an actual hydrolysis or (c) a combined hydrolysis and fermentation (CHF) process. Initial adsorption of the cellulases onto the substrate can be used to determine the minimal cellulase requirements for efficient hydrolysis since enzymes initially adsorbed to the substrate have a strong role in governing the overall reaction. Trichoderma harzianum E58 produces high levels of -glucosidase and is able to cause high conversion of Solka Floc BW300 to glucose without the need for exogenous -glucosidase. End-product inhibition of the cellulase and -glucosidase can be more effectively reduced by employing a CHF process than by supplemental -glucosidase.Offprint requests to: C. M. Hogan     

Cerebrospinal fluid gradients of acetylcholinesterase and butyrylcholinesterase activity in healthy aging

Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities were measured in 13 sequential 2 ml aliquots of cerebrospinal fluid (CSF) obtained by lumbar puncture from 7 young and 7 elderly healthy normal subjects. The slopes of the rostrocaudal gradients of AChE and BChE were calculated and compared to those of total protein concentration and the major dopaminergic metabolite homovanillic acid (HVA), for which a pronounced rostrocaudal gradient (with highest concentrations of HVA in more rostral CSF) is consistent with HVA originating primarily from the brain. AChE activity was higher in more caudal fractions of young, but not elderly subjects and there was a significant difference between the mean AChE gradient slopes in the young and old groups. These results suggest that the spinal cord makes an important contribution to AChE activity in lumbar CSF. Furthermore, the absence of a negative AChE gradient in elderly subjects may be the result of a greater rate of entry of cerebral AChE into CSF, possibly as a consequence of an increased ventricular surface area and shorter diffusion distances in atrophic elderly brains. In contrast to AChE, BChE activity and total protein concentrations were higher in more caudal CSF fractions of not only young but also old subjects. In addition, there was a significant correlation between the gradient slopes of BChE activity and total protein concentrations, suggesting that the majority of BChE activity in lumbar CSF derives from the same source as the majority of total protein, namely plasma. The diffuse (i.e. brain and spinal cord) origin of AChE in lumbar CSF would explain the relatively modest changes in lumbar CSF AChE activity in diseases involving certain central cholinergic systems, most notably Alzheimer's disease.     

Lipid production of revertants of Ufa mutants from the oleaginous yeast Apiotrichum curvatum

Summary From six unsaturated fatty acid auxotrophs (Ufa mutants) of the oleaginous yeast Apiotrichum curvatum blocked in the conversion of stearic to oleic acid, were isolated revertants able to grow in the absence of unsaturated fatty acids, in a search for strains that can produce cocoa butter equivalents. A broad range in the percentage of saturated fatty acids (%SFA) was observed in the lipids of individual revertants (varying from 27%–86% SFA), compared with the wild-type (44% SFA). Further analysis of fatty acid composition indicated that: (i) not all six Ufa mutants had the same genetic background and (ii) one specific Ufa mutation could be reverted in more than one way. Revertants that produced lipids with a %SFA>56%, were examined further. These strains were cultivated for 50 generations and half of them produced lipids with high %SFA after that time and were defined as stable. The viability of revertant strains with extremely high %SFA (>80%) may be explained by our finding that polar lipids, which are part of yeast membranes, contained much more polyunsaturated fatty acids and a significantly lower %SFA than neutral (storage) lipids. One revertant (R25.75) was selected that was able to produce lipids in whey permeate at a rate comparable with wild-type A. curvatum and with a fatty acid composition and congelation curve comparable with cocoa butter. Offprint requests to: A. Ykema     

Growth and development of biofeedback: A bibliographic update

Computerized literature searching techniques were used to examine publication patterns in the worldwide biofeedback literature. Searches were completed in the United States and in Japan for the years 1985 through 1987. The results were used to update the results of an earlier study (Hatch & Riley, 1985) that covered the years from 1964 through 1984. Publication growth curves were generated for several media, including scientific journal articles, books, doctoral dissertations, and popular magazine articles. Although publication of information about biofeedback remains active worldwide, there has been a declining trend in effect for the past several years. The American database grossly underestimated the number of Japanese biofeedback articles, and it is likely that the literatures of other countries outside of North America were similarly underestimated. Possible explanations for the various trends noted are discussed.These results were presented in part at the Twentieth Annual Meeting of the Association for Applied Psychophysiology and Biofeedback. We gratefully acknowledge the assistance of Margaret Cyr-Provost in preparing the data for analysis.     

Density-induced down regulation of epidermal growth factor receptors

Summary Previous studies have shown that cell density can regulate the binding of several growth factors. To determine whether cell density exerts a uniform effect on the expression of epidermal growth factor (EGF) receptors, seven cell lines were examined in detail. For each cell line, EGF binding was found to decrease as cell density increases. Scatchard analysis of the binding data reveals that decreases in EGF binding are due to reductions in the number of cell surface EGF receptors. The only apparent exception is the effect of cell density on the binding of EGF to A-431 cells. For these cells, increases in cell density lead to two effects: decreases in the number of high affinity EGF receptors and increases in the total number of EGF receptors. In addition to the effects of cell density on EGF receptors, it was determined that increases in cell density can coordinately down-regulate receptors for as many as four different growth factors. Overall, the findings described in this report for EGF and those previously described for transforming growth factor type-β (TGF-β) and fibroblast growth factor (FGF) demonstrate the existence of a common mechanism for down-regulating growth factor receptors. This work was supported by grants from the Nebraska Department of Health (89-51), the National Cancer Institute (Laboratory Research Center Support Grant, CA36727), and the American Cancer Society (Core Grant ACS SIG-16). EDITOR'S STATEMENT The paper by Rizzino et al. demonstrates that receptor number decreases as a function of cell density. This may represent a mechanism by which cell proliferation is reduced as cell density increases.     

Psychophysiological responsivity on a laboratory stress task: Methodological implications for a stress-muscle hyperactivity pain model

A stress-muscle hyperactivity-pain (SMP) model has been proposed to explain the etiology of certain musculoskeletal pain disorders. According to this model, subjects should show physiological arousal during periods of stress relative to periods of rest. In a test of this prediction, 31 subjects performed a reaction time task that has been used in previous laboratory studies. Multiple psychophysiological variables were monitored during initial and final 10-minute baselines, during performance on nine 2-minute reaction time tasks, and during 36-second rest intervals following each of the 2-minute tasks. Results showed small but statistically significant differences generally supporting the SMP model when masseter EMG was averaged over time periods of 12 seconds to 2 minutes, but not when masseter EMG was averaged over 10- to 18-minute blocks. These results demonstrated the importance of carefully selecting time intervals for analysis. Additional analyses that compared TMD with symptom-free subjects revealed small differences in EMG that supported the SMP model. Analyses of EMG over shorter time intervals also showed, however, that masseter EMG increased during the 36-second rest interval following performance on a 2-minute stress task; this result suggested that a modification of the SMP model may be necessary.This research was supported in part by Grant 2 S06RR08038-17 funded by the National Institutes of Health.     

Bleomycin-Iron Damage To Dna With Formation Of 8-Hydroxydeoxyguanosine and Base Propenals. Indications That Xanthine Oxidase Generates Superoxide From Dna Degradation Products

Bleomycin, in the presence of ferric salts, oxygen and a suitable reductant, degrades DNA with the release of base propenals, detected as thiobarbituric acid (TBA) reactivity, and the formation of 8-hydroxydeo-xyguanosine (80HdG) detected by HPLC. When xanthine oxidase is added to the incubated mixture of DNA degradation products, TBA-reactivity is destroyed but 80HdG formation is increased. EPR Spin trapping experiments show that hydroxyl radicals (OH) are formed in the reaction mixture and can be inhibited by the inclusion of either superoxide dismutase or catalase. These findings suggest that the base propenals and possibly malondialdehyde, formed from them, are aldehydic substrates for xanthine oxidase and, the product of this reaction is superoxide (O₂^-) and hydrogen peroxide (H₂O₂). Thus, TBA reactivity is destroyed in the formation of O₂^- and H₂O₂ which stimulate further oxidative damage to DNA resulting in increased 8OHdG formation.