Although iron is the fourth most abundant element in the Earth's crust, bioavailable iron limits marine primary production in about one third of the ocean. This lack of iron availability has implications in climate change because the removal of carbon dioxide from the atmosphere by phytoplankton requires iron. Using literature values for global fish biomass estimates, and elemental composition data we estimate that fish biota store between 0.
View Article and Find Full Text PDFThe core structure of the photosynthetic reaction center is quasisymmetric with two potential pathways (called A and B) for transmembrane electron transfer. Both the pathway and products of light-induced charge separation depend on local electrostatic interactions and the nature of the excited states generated at early times in reaction centers isolated from Rhodobacter sphaeroides. Here transient absorbance measurements were recorded following specific excitation of the Q(y)() transitions of P (the special pair of bacteriochlorophylls), the monomer bacteriochlorophylls (B(A) and B(B)), or the bacteriopheophytins (H(A) and H(B)) as a function of both buffer pH and detergent in a reaction center mutant with the mutations L168 His to Glu and L170 Asn to Asp in the vicinity of P and B(B).
View Article and Find Full Text PDFThe extent of electrostatic contributions from the protein environment was assessed by the introduction of ionizable residues near the bacteriochlorophyll dimer in reaction centers from Rhodobacter sphaeroides. Two mutations at symmetry-related sites, M199 Asn to Asp and L170 Asn to Asp, resulted in a 48 and 44 mV lowering of the midpoint potential, respectively, compared to the wild type at pH 8, while a 75 mV decrease in the midpoint potential was observed for the mutation L168 His to Glu. The decrease relative to wild type was found to be approximately additive, up to 147 mV, for various combinations of the mutations.
View Article and Find Full Text PDFThe core of the photosynthetic reaction center from the purple non-sulfur bacterium Rhodobacter sphaeroides is a quasi-symmetric heterodimer, providing two potential pathways for transmembrane electron transfer. Past measurements have demonstrated that only one of the two pathways (the A-side) is used to any significant extent upon excitation with red or near-infrared light. Here, it is shown that excitation with blue light into the Soret band of the reaction center gives rise to electron transfer along the alternate or B-side pathway, resulting in a charge-separated state involving the anion of the B-side bacteriopheophytin.
View Article and Find Full Text PDFCross-sectional studies of humans have shown that dehydroepiandrosterone sulfate (DHEAS) peaks shortly after sexual maturation and declines thereafter, suggesting that the progressive reduction in DHEAS may play a role in the aging process and in the development of age-related morbidity. The present study examines changes in DHEAS concentrations across the life span of rhesus monkeys as part of the development of this primate model for studies of aging. Serum concentrations of DHEAS were measured in 792 laboratory-housed rhesus monkeys (Macaca mulatta) aged 0.
View Article and Find Full Text PDFMacaque laboratory chows provide relatively more calcium (Ca) and vitamin D (D) than human diets; this may influence skeletal aging. To evaluate this possibility, parameters of skeletal relevance in premenopausal and naturally postmenopausal rhesus monkeys were measured in a cross-sectional study. Serum osteocalcin (Oc) was elevated in the postmenopausal group (P < 0.
View Article and Find Full Text PDFTo further characterize the skeletal role of vitamin K (K), markers of bone turnover, density, and strength were evaluated in rats with diet- or warfarin (W)-induced K insufficiency. One hundred two, 7-week-old, female rats were randomly assigned to low K (phylloquinone [K1], 20 microg/kg diet), control K (K1, 1300 microg/kg diet), low-dose W (W, 1.5 mg/kg control diet), or high-dose W plus K (W/K1, 10/100 mg/kg diet).
View Article and Find Full Text PDFOsteoarthritis (OA) spuriously elevates spine bone mineral density (BMD) as measured by dual-energy X-ray absorptiometry (DXA). This study documents spinal OA prevalence in adult female rhesus monkeys, and evaluates a custom central region-of-interest (CROI) analysis technique designed to minimize OA effects on BMD measurement. Lumbar spine radiographs were obtained on 71 animals, age 10-37 years.
View Article and Find Full Text PDFThis study assessed effects of the bisphosphonate zoledronate (ZLN) on bone density and biochemical markers of bone turnover in ovariectomized (OVX) adult female rhesus monkeys. Forty monkeys were randomly assigned to one control or four OVX groups. The control and one OVX group received saline, and the other three OVX groups received ZLN (0.
View Article and Find Full Text PDFDehydroepiandrosterone (DHEA) lowers serum cholesterol, particularly the low density lipoprotein (LDL) fraction, in rhesus monkeys on a commercial diet (12% calories from fat, 0.0083% cholesterol). We fed rhesus monkeys a diet of 30% calories from fat and 0.
View Article and Find Full Text PDFThe effect(s) of exogenous dehydroepiandrosterone (DHEA) was studied in healthy non-obese rhesus monkeys. Six monkeys were given 60 mg/kg/day DHEA for 4 weeks. The dose was then increased to 75 mg/kg/day for an additional 4 weeks.
View Article and Find Full Text PDFWe studied the effect(s) of exogenous dehydroepiandrosterone (DHEA) in spontaneously obese dogs. Nineteen euthyroid obese and six non-obese normal dogs were evaluated. Dogs received DHEA for three months at an escalating dose of 30-75 mg/kg p.
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