State transitions,photosystem stoichiometry adjustment and non-photochemical quenching in cyanobacterial cells acclimated to light absorbed by photosystem I or photosystem II

Cells of the cyanobacterium Synechococcus 6301 were grown in yellow light absorbed primarily by the phycobilisome (PBS) light-harvesting antenna of photosystem II (PS II), and in red light absorbed primarily by chlorophyll and, therefore, by photosystem I (PS I). Chromatic acclimation of the cells produced a higher phycocyanin/chlorophyll ratio and higher PBS-PS II/PS I ratio in cells grown under PS I-light. State 1-state 2 transitions were demonstrated as changes in the yield of chlorophyll fluorescence in both cell types. The amplitude of state transitions was substantially lower in the PS II-light grown cells, suggesting a specific attenuation of fluorescence yield by a superimposed non-photochemical quenching of excitation. 77 K fluorescence emission spectra of each cell type in state 1 and in state 2 suggested that state transitions regulate excitation energy transfer from the phycobilisome antenna to the reaction centre of PS II and are distinct from photosystem stoichiometry adjustments. The kinetics of photosystem stoichiometry adjustment and the kinetics of the appearance of the non-photochemical quenching process were measured upon switching PS I-light grown cells to PS II-light, and vice versa. Photosystem stoichiometry adjustment was complete within about 48 h, while the non-photochemical quenching occurred within about 25 h. It is proposed that there are at least three distinct phenomena exerting specific effects on the rate of light absorption and light utilization by the two photoreactions: state transitions; photosystem stoichiometry adjustment; and non-photochemical excitation quenching. The relationship between these three distinct processes is discussed.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F relative fluorescence intensity at emission wavelength nm - F _o fluorescence intensity when all PS II traps are open - light 1 light absorbed preferentially by PS I - light 2 light absorbed preferentially by PS II - PBS phycobilisome - PS photosystem     

Heat-shock cognate protein (hsc71) and related proteins in mouse spermatogenic cells

A monoclonal antibody (13D3) has been developed that recognizes a 71 kilodalton (71 kDa) protein on two-dimensional immunoblots of proteins extracted from a mixture of mouse spermatogenic cells (mainly pachytene spermatocytes and spermatids). This protein was shown by immunoblotting and adenosine triphosphate (ATP)-binding characteristics to be identical to a 71 kDa mouse heat-shock cognate (hsc) protein, hsc71, present in 3T3 cells. Along with a 70 kDa heat-shock inducible protein (hsp70), and a 74 kDa heat-shock cognate protein (hsc74), hsc71 is a product of the mouse HSP70 multigene family. Although antibody 13D3 reacted strongly with hsc71, it reacted only faintly with hsp70 in 3T3 cells, and not at all with hsc74 or a germ cell-specific hsp70-like protein (P70) on immunoblots of mixed germ cells. Antibody 13D3 is unique among known antibodies in its pattern of reaction with these heat-shock proteins. In immunofluorescence studies on isolated germ cells, 13D3 reacted uniformly with the cytoplasm of pachytene spermatocytes, round spermatids, and residual bodies, but only with the midpiece of spermatozoa. Antibody 13D3 recognizes other proteins in addition to hsc71 on two-dimensional immunoblots of condensing spermatids and spermatozoa. Two of the proteins (70 kDa/pI 6.4 and 70 kDa/pI 6.5) were present in condensing spermatids and spermatozoa, and another protein (69 kDa/pI 7.0) was detected only in spermatozoa. The new proteins also were recognized by monoclonal antibody 7.10, which reacts specifically with hsp70, hsc71, hsc74, and P70. Although [35S]methionine was incorporated into the new proteins in condensing spermatids, hsc71, hsc74, and P70 were not labeled. These results suggest that unique heat-shock proteins are synthesized late in spermatogenesis.     

Some pharmacological activities of novel adenine-related compounds isolated from a marine sponge Agelas mauritiana

Agelasimine A and agelasimine B, two novel compounds related to adenine, have been isolated from the orange sponge, Agelas mauritiana, and have been tested for a variety of biological activities. Both compounds inhibited proliferation of cultured L1210 leukemia cells at nanomolar concentrations with accumulation in the G1 stage of the cell cycle. However, no prolongation of life was observed in mice bearing P388 leukemia treated with these compounds. In the rat isolated aorta, micromolar concentrations of agelasimines were very effective in inhibiting contractions elicited by potassium chloride but had little or no effect on responses for prostaglandin F2 alpha and had modest effects on the responses to noradrenaline and significant effects on 5-hydroxytryptamine. Agelsamines A and B appeared to be equipotent in causing relaxation in rabbit jejunum and bovine coronary artery, and they also inhibited nucleoside transport into rabbit erythrocytes in micromolar concentrations.     

Evidence for chromosomal replicons as units of sister chromatid exchanges

Chromosomal replicons have been described as the cytological counterpart of DNA replicon clusters and have previously been studied in vitro using premature chromosome condensation-sister chromatid differentiation (PCC-SCD) techniques. Chromosomal replicons are visualized as small SCD segments in S-phase cells, and measurement of these segments can provide estimates of relative chromosomal replicon size corresponding to DNA replicon clusters functioning coordinately in S-phase. Current hypotheses of sister chromatid exchange (SCE) formation postulate that sites of SCE induction are associated with active replicons or replicon clusters. We have applied the PCC-SCD technique to in vivo studies of mouse bone marrow cells that have been treated with cyclophosphamide (CP) for two cell cycles. We have been able to visualize chromosomal replicons, as well as SCEs which have been induced in vivo by CP treatment, simultaneously in the same cells. Chromosomal replicons visualized as small SCD segments were measured in PCC cells classified at early or late S-phase based on SCD segment size prevalence. Early S-phase (E/S) PCC cells contained 90% of the SCD segments measured clustered in a segment size range of 0.1 to 0.8 m with a peak value around 0.3 to 0.6 m regardless of CP treatment. As the cells progressed through S-phase, late S-phase (L/S) PCC cells were characterized by the appearance of larger SCD segments and even whole SCD chromosomes in addition to small SCD segments. A concentration of units around 0.4 to 1.0 m was found for L/S SCD segment size distributions regardless of CP treatment with an apparent bimodal profile. Our in vivo data support the existence of a subunit organization of chromosomal replication with a basic functional unit being 0.3 to 0.6 m in size. In addition, we have found that this chromosomal unit of replication or chromosomal replicon does not seem to be functionally perturbed by the mutagen CP. We also found that small SCD segments of 0.4 to 0.7 m in length were involved in the formation of an SCE, suggesting that both spontaneous and CP-induced SCEs occur between chromosomal replicons. These findings provide direct cytogenetic evidence to support a replicon cluster/chromosomal replicon model for SCE formation.     

Principal/agent theory and decision making in health care

Principal/agent theory, an economics concept that defines an agency relationship as "a contract under which one or more persons engage another person (the agent) to perform some service on their behalf which involves delegating some decision-making authority to the agent," is held to be applicable to the patient/physician relationship, in contrast to the view that this is a fiduciary relationship, not a contractual one. The distinction between fiduciary and contractual relationships is illuminated in the process of evaluating objections to the application of the principal/agent theory to the patient/physician relationship. The ability of the principal/agent theory to reveal important features of advance directives, understood as public documents rather than as confidential instructions from patient to physician, is also examined.     

A novel hsp70-like protein (P70) is present in mouse spermatogenic cells.

Mouse spermatogenic cells contain relatively large amounts of a 70-kilodalton protein (P70) that is closely related to hsp70, the major inducible heat shock protein. When hsp70 from spermatogenic cells is heat induced, it migrates to the same location as does P70 on two-dimensional polyacrylamide gels, indicating that it has an apparently identical mass and isoelectric point. P70 reacts strongly and specifically with an anti-Drosophila hsp70 monoclonal antibody that is specific for products of the hsp70 gene family. Both P70 and hsp70 are also ATP-binding proteins and are purified by using ATP-affinity chromatography. However, P70 and hsp70 are unique proteins on the basis of peptide map analysis and are regulated differently in germ cells. P70 appears to be a novel heat shock protein of spermatogenic cells which is synthesized in association with germ cell differentiation.     

Copper deficiency depresses rat aortae superoxide dismutase activity and prostacyclin synthesis

Prostaglandin synthesis shows dependence on lipid hydroperoxides and resultant oxygen derived radical formation. In view of the importance of dietary copper in cytosolic copper dependent superoxide dismutase (Cu/Zn SOD) activity and the role of SOD in oxygen radical formation, the influence of dietary copper on prostacylin (PGI2) synthesis and SOD activity in rat aorta was examined. Copper deficient (0.5 micrograms Cu/g diet) rats showed a significant 47% reduction in PGI2 synthesis rates by aortic ring incubations in comparison to copper adequate (6.0 micrograms Cu/g diet) animals. Aortic SOD activity was reduced by 46% in copper deficiency in comparison to copper adequate animals. Marginal dietary copper (1.6 micrograms Cu/g diet) significantly reduced aortic SOD activity by 32% but was without effect on aortic ring incubation PGI2 synthesis. These results indicate that dietary copper deficiency, and the resultant decrease in SOD activity, depresses aortic PGI2 synthesis.