ESR and ENDOR of primary reactants in photosynthesis

The primary reactants in photosynthesis are defined as the chemical entities on which charges are generated and stabilized after capture of a photon by the photochemical trap: PIX ^hv P ^* IX P ⁺ I ^– X P ⁺ IX ^–, where P stands for the primary electron donor, P ^* for its excited singlet state, I for the first (ESR-detectable) electron acceptor and X for the secondary acceptor complex. The ESR and ENDOR experiments which have played a rÔle in the identification and characterization of P, I, and X in the bacterial and plant photosystems are comprehensively reviewed. The structural and kinetic information obtained with magnetic resonance techniques are integrated with results obtained with optical spectroscopy to give a unified picture of the pathway of primary photochemistry in photosynthesis. Nomenclature of Primary Reactants In the interest of uniformity this review introduces a nomenclature of the primary reactants that deviates in some respects from the commonly used labels. The nametags used here and listed below are abbreviations of the molecules that are identified as primary reactants, with the exception of the donors, for which I have retained the commonly accepted designation. Photosystems: PS 1, photosystem 1 of plants; PS 2, photosystem 2 of plants; pBPS, the photosystem of purple bacteria; gBPS, ditto of green bacteria. P: Primary donors: P700 (PS 1), P680 (PS 2), P860 (generic label for BChl a containing purple bacteria), P960 (generic label for BChl b containing purple bacteria), P840 (generic name for green bacteria). I: First acceptors: Chl a (PS 1), Ph a (PS 2), BPh a,b (pBPS). X: Secondary acceptors: F _x (PS 1), pQ ₁ (PS 2), uQ ₁ or mQ ₁ (pBPS), B (gBPS). Tertiary acceptors: F _A,B (PS 1), pQ ₂ (PS 2), uQ ₂ (pBPS), F ₁ (gBPS).This paper is based on a lecture given at the Joint Meeting of the Belgium, German (FRG), and Netherlands Societies for Biophysics, Aachen 1980     

Value of 1-alpha-hydroxy vitamin D3 in treatment of primary hyperparathyroidism before parathyroidectomy.

The postoperative course of six patients with primary hyperparathyroidism and obvious radiological evidence of bone disease pretreated with 1-alpha-hydroxy vitamin D3 (1 alpha HCC) was indistinguishable from that of six patients with a similar clinical and radiological picture who were not pretreated. 1alphaHCC may increase the hypercalcaemia in some cases and cannot be recommended for the routine preparation of such patients for surgery.     

Local cold exposure of Andean Indians during normal and simulated activities.

Thermal resonses of Andean Indians were measured during several customary tasks associated with cold exposure in the highlands of southern Peru. These included surface temperature measurements of women while they washed clothing in the river and similar measurements of men while they constructed a diversion channel in the same river. A third test measured the effects of alcohol consumption on body temperatures during light activity. Women maintained slightly warmer hand than foot temperatures. Men maintained nearly equal hand and foot temperatures during the exposure period. Among male subjects the foot rewarmed at a faster rate than the hand. The results from the field studies compared favorably with results from earlier laboratory exposure tests. Comparisons between the river water exposure tests for males and females showed a consistent pattern where females maintained warmer hand and foot temperatures than males. These findings were in accord with previous laboratory studies among Quechua Indians and with the findings reported for other ethnic groups who experience natural cold stress. Alcohol ingestion appeared to have minimal effect in mitigating cold stress response during light activity. This finding was counter to earlier laboratory tests of resting subjects.     

Pseudomonas aeruginosa polysaccharide Psl supports airway microbial community development

Pseudomonas aeruginosa dominates the complex polymicrobial cystic fibrosis (CF) airway and is a leading cause of death in persons with CF. Oral streptococcal colonization has been associated with stable CF lung function. However, no studies have demonstrated how Streptococcus salivarius, the most abundant streptococcal species found in individuals with stable CF lung disease, potentially improves lung function or becomes incorporated into the CF airway biofilm. By utilizing a two-species biofilm model to probe interactions between S. salivarius and P. aeruginosa, we discovered that the P. aeruginosa exopolysaccharide Psl promoted S. salivarius biofilm formation. Further, we identified a S. salivarius maltose-binding protein (MalE) that is required for promotion of biofilm formation both in vitro and in a Drosophila melanogaster co-infection model. Finally, we demonstrate that promotion of dual biofilm formation with S. salivarius is common among environmental and clinical P. aeruginosa isolates. Overall, our data supports a model in which S. salivarius uses a sugar-binding protein to interact with P. aeruginosa exopolysaccharide, which may be a strategy by which S. salivarius establishes itself within the CF airway microbial community.Subject terms: Bacteriology, Biofilms, Microbiome, Clinical microbiology     

The active site cysteine of ubiquitin-conjugating enzymes has a significantly elevated pKa: functional implications

Ubiquitin-conjugating enzymes (E2s or Ubcs) are essential components in the ubiquitination apparatus. These enzymes accept ubiquitin from an E1 enzyme and then, usually with the aid of an E3 enzyme, donate the ubiquitin to the target protein. The function of E2 relies critically on the chemistry of its active site cysteine residue since this residue must form a thioester bond with the carboxyl terminus of ubiquitin. Despite the plethora of structural information that is available, there has been a notable dearth of information regarding the chemical basis of E2 function. Toward filling this large void in our understanding of E2 function, we have examined the pK(a) of the active site cysteine using a combination of experimental and theoretical approaches. We find, remarkably, that the pK(a) of the active site cysteine residue is elevated by approximately 2 pH units above that of a free cysteine. We have identified residues that contribute to the increase in this pK(a). On the basis of experimental values obtained with three different E2 proteins, we believe this to be a general and important characteristic of E2 protein chemistry. Sequence comparison suggests that the electrostatic environment is maintained not through strict residue conservation but through different combinations of residues near the active site. We propose that the elevated pK(a) is a regulatory mechanism that prevents the highly exposed cysteine residue in free E2 from reacting promiscuously with electron deficient chemical moieties in the cell.