Application of a photosystem II model for analysis of fluorescence induction curves in the 100 ns to 10 s time domain after excitation with a saturating light pulse

A mathematical model of photosystem II (PSII) events was used to analyze chlorophyll fluorescence transients in the time domain from 100 ns to 10 s after excitation with a saturating 10-ns flash, applied as a part of specialized illumination protocol, using preparations of a thermophilic strain of the unicellular green alga, Chlorella pyrenoidosa Chick (using both intact and diuron-treated cells). Analysis of simulation results has proven that particular attention should be given to flash-induced recombination processes, including nonradiative recombination in PSII, while subsequent charge transfer along the electron transport chain of thylakoid membrane can be adequately described by a single reaction of quinone reoxidation. The PSII model was extended by taking inhibition by diuron of the electron transport in the acceptor side of PSII into account, which allowed simulation of fluorescence induction curves observed in the presence of this inhibitor. The model parameters were determined (stromal pH, rate constants of nonradiative recombination, and the initial reduction state of the quinone pool) which provided adequate simulation of experimentally observed ratios of the maximal and initial fluorescence levels (F _m/F ₀).     

On feeding and nutrition in Fungiacava eilatensis (Bivalvia, Mytilidae), a commensal living in fungiid corals

The enlarged inhalant siphon of Fungiacava eilatensis opens into the coelenteron of species of fungiid corals with which it lives in commensal association. Material consisting of mucus, zooxanthellae, nematocysts, plankton and inorganic matter, is taken exclusively from the coelenteron. The very mobile foot possibly assists in food collection and in the removal of pseudofaeces; but, with large ctenidia, the bivalve is a typical ciliary feeder. Experiments with labelled zooxanthellae reveal that these are taken into the gut of Fungiacava with subsequent metabolic incorporation of products derived from them. The other prime source of food must be phytoplankton carried in with the feeding currents of the coral, itself carnivorous so that there is no competition for food between commensal and host. The Fungia zooxanthella– Fungiacava association operates as a "Troika" the productivity of which is autoregulated in proportion to the number of bivalves present. The inorganic wastes of the bivalve (as well as those of the coral) are utilized by the zooxanthellae, resultant increase in the algal component becoming available as food to the bivalve. Losses in the cycle are balanced by intake of exogenous food.     

Reduced sensitivity of peripheral cells to glucocorticoids in hypercholesterolemia

It has been found that lymphocytes of hypercholesterolemic (HCh) subjects are characterized by a reduced number of glucocorticoid receptors (GcR) as compared with the cells of normolipidemics (N). Addition of HCh-sera or very low density lipoproteins, or low density lipoproteins isolated both from HCh-sera and N-sera to cultured human skin fibroblasts brought about a fall in the number of GcR in the cells. High density lipoproteins had no effect on GcR level. Dexamethasone was less effective in inhibiting cholesterol synthesis from [14C]acetate in the lymphocytes and fibroblasts with a reduced number of GcR. In the presence of dexamethasone (I x 10(-8)M) in fibroblast growth medium, reduced number of GcR (due to preincubation with very low density lipoproteins) led to a substantial increase in cholesterol synthesis. These findings indicate that the sensitivity of peripheral cells to glucocorticoids is decreased in HCh which might be one of the trigger mechanisms of atherogenesis.     

Population analysis of minor hemoglobin fractions. I. Hemoglobin A2]

The inhabitants of 7 isolated villages (of different nationalities) and of 5 panmictic populations were studied. Populational and segregation analyses of Hb A2 in 3036 normal and 150 heterozygous individuals for beta- and delta beta-thalassemia were carried out. The Hb A2 levels in some populations are established to deviate from the normal distribution. Bimodal dependency of the levels of Hb A2 distribution is demonstrated, which suggests the existance of heterogenous subpopulations by the Hb A2 level. The segregation analysis has revealed distinct genetic determination of Hb A2 levels. There was a good correlation between Hb A2 and Hb F values (r=-0.82).