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     

In vivo administration of Fab' fragments of anti-L3T4 (GK1.5) antibody inhibits the T helper cell function of murine lymph node cells

The effect of intravenous injection of Fab' fragments of anti-L3T4 antibody (GK1.5 monoclonal antibody) into mice was studied. This treatment depleted L3T4+ cells from the popliteal lymph nodes of keyhole-limpet hemocyanin-primed mice. The T cells that remained were unable to provide help to antigen-specific B cells in vitro. The results obtained using Fab' fragments were comparable with those using intact anti-L3T4 antibody and demonstrate that either form of GK1.5 is a potentially useful immunosuppressive agent in mice.     

Vitamin K-dependent carboxylase: influence of the "propeptide" region on enzyme activity

The liver microsomal vitamin K-dependent carboxylase catalyzes the post-translational conversion of specific glutamyl to gamma-carboxyglutamyl (Gla) residues in precursor forms of a limited number of proteins. These proteins contain an amino-terminal extension (propeptide) that is presumed to serve as an enzyme recognition site to assure their normal processing. The free, noncovalently bound propeptide has also been shown to stimulate the in vitro activity of this enzyme. This peptide has now been shown to lower the app Km of a low-molecular-weight Glu site substrate while having no influence on the app Km of the other substrates, vitamin KH2, O2, and CO2/HCO3-. Propeptide addition was shown to have no influence on the ratio of the two products of the enzyme, Gla and vitamin K-2,3-epoxide. Stimulation of carboxylase activity by the propeptide from human factor X was observed in a number of rat tissues and in the liver of a number of different species. Stability of the enzyme in crude microsomal preparations was greatly enhanced by the presence of propeptide. These observations are consistent with the hypothesis that this region of the protein substrates for the carboxylase not only serves an enzyme recognition or docking function but also modulates the activity of the enzyme by altering the affinity for one of its substrates.     

Patterns of energy storage in Pseudoboeckella poppei (Crustacea,copepoda) from two contrasting lakes on Signy Island,Antarctica

The copepod Pseudoboeckella poppei (Daday) (Calanoida, Centropagidae) was sampled from Sombre and Heywood Lakes on Signy Island, Antarctica (60° S, 45° W) between January 1984 and March 1985. Sombre Lake is clear and oligotrophic with little phytoplankton and a bottom sediment low in organic content. By contrast Heywood Lake is turbid and mesotrophic; a substantial phytoplankton develops in summer and the bottom sediments are comparatively rich in organics. Both lakes freeze over for much of the year, forcing the copepods to adopt a benthic feeding strategy over winter. Adult Pseudoboeckella feed on phytoplankton when this is available, but also on detritus, diatoms and short algal filaments stirred up from the sediment. In Heywood Lake, male copepods show a smooth seasonal trend in lipid content with lipid being synthesised in early summer and utilised in late summer and winter. The summer increase in lipid content is associated with an increase in dry weight. Female lipid contents show evidence of two peaks of egg production. In Sombre Lake both male and female copepods increase in size during summer and show a wider range of lipid contents than in Heywood Lake; it is likely that this is due to the poorer winter feeding conditions which necessitate the synthesis of a much larger store of reserves during the summer. In contrast to marine calanoid copepods, lipid stores are exclusively triacylglycerol with no trace of wax ester.     

An appraisal of bioassay methods for the detection of mycotoxins—a review

The literature on bioassay methods for mycotoxin detection has been reviewed. An outline of the range of bioassay methods is given and the role of cytotoxicity tests in particular has been emphasized.     

Investigation of transport-associated phosphorylation of sugar in yeast mutants (snf3) lacking high-affinity glucose transport and in a mutant (fdp1) showing deficient regulation of initial sugar metabolism

Pool-labeling experiments with 2-deoxyglucose in derepressed cells of the yeastSaccharomyces cerevisiae confirmed the previously reported results pointing to the possible existence of transport-associated phosphorylation of sugar. In yeast mutants containing a disruption or an inactivating point mutation in thesnf3 gene, which codes for the high-affinity glucose carrier, no evidence for transport-associated phosphorylation of 2-deoxyglucose was observed. If transport-associated phosphorylation in yeast exists, it is apparently not mediated by the low-affinity glucose carrier. Mediation by the high-affinity carrier would fit with the known requirement of an active kinase for high-affinity sugar transport. A mixed type of uptake in cells having both carriers would explain many of the problems associated with the 2-deoxyglucose pool-labeling experiments. Since mutants that have only low-affinity glucose transport are not deficient in the glucose-induced RAS-mediated cAMP signal, transport-associated phosphorylation of glucose is not required for or involved in the induction of the signal. The yeastfdp mutant, which dies on media containing fermentable sugars because of overaccumulation of sugar phosphates, also did not show any evidence for the existence of transport-associated phosphorylation. The same was true for the double mutantfdp snf3. The latter also showed the typicalfdp phenotype, indicative that the lethality on media containing fermentable sugar is owing to aberrant regulation of low-affinity transport. The high protein kinase activity in thefdp mutant does not appear to be responsible for the absence of evidence for transport-associated phosphorylation, because another mutant with high protein kinase activity, thebcy mutant, displayed normal transport behavior.     

Cellular localization of ovarian proopiomelanocortin messenger RNA during follicular and luteal development in the rat

Opioid peptides are expressed in the reproductive system and have been reported to regulate reproductive function. The present study used in situ hybridization to selectively localize ovarian cells containing high levels of proopiomelanocortin (POMC) mRNA, an opioid precursor, during different stages of ovarian development. Prepubertal rats were primed with PMSG to stimulate follicular development, followed by hCG to induce ovulation. Treatment groups consisted of control (no treatment), PMSG (2 days post-PMSG), 1 day corpus luteum (CL; 1 day post-hCG), and 8 day CL (8 days post-hCG). POMC mRNA-containing cells were present in antral follicles, CL, and the interstitial compartment. With gonadotropin treatment, the percentage of follicles containing heavily labeled cells increased in the PMSG and 1 day CL groups. The number of POMC mRNA-containing cells per follicle also increased in the 1 day CL group. In the CL, no difference was observed in the percentage of CL exhibiting labeled cells between the 1 day CL and 8 day CL groups; however, more labeled luteal cells per CL were present in the 1 day CL group. A marked increase in POMC mRNA-containing cells was observed in the interstitial compartment of the 1 day CL group. These results indicate that the number of POMC mRNA-containing cells increases with follicular development and CL formation; however, the ovarian distribution suggests that the labeled cells could be nonendocrine cells, possibly white blood cells. The in situ hybridization findings are indicative of low total concentrations of ovarian POMC mRNA, suggesting mainly an autocrine or paracrine role for POMC or POMC-derived peptides.(ABSTRACT TRUNCATED AT 250 WORDS)     

The endogenous lectins of the chick blastoderm are present in association with an apolipoprotein in distinct organelles and in the extracellular matrix

Summary Affinity purified preparations of the galactose-binding lectin from gastrulating chick blastoderms consist of three main polypeptides. Two of these have been identified as the 14 kD and 16 kD galactose-binding lectins. A third one migrates in SDS-PAGE gels with a relative molecular weight of 6,500±500 and has been identified as an apolipoprotein (Apo) of plasma very low density lipoproteins, Apo-VLDL-II. We have studied the localization of these polypeptides using immunofluorescence and ultrastructural immunocytochemistry with peroxidase and protein-A gold. The 14 kD lectin occurs in the intracellular yolk where it is mainly present within the electron lucent component. The 16 kD is also present in the intracellular yolk platelets, but tends to predominate in the electron-dense component. In addition, the 16 kD lectin is also present in pleiomorphic yolk-associated organelles and in the extracellular matrix. Apo-VLDL-II is also localized in the electron-lucent component of the yolk platelet and in the extracellular matrix. Our results suggest that the lectin(s) are associated with Apo-VLDL-II in the yolk platelet, and may subsequently become externalized.     

The Upper Cave at Zhoukoudian and the origins of the Mongoloids

The best evidence for identifying the inhabitants of northeast Asia in the terminal Pleistocene or early Holocene periods is provided by the human burials from the Upper Cave at Zhoukoudian, and in particular the “Old Man”. Apart from the Minatogawa finds on Okinawa, all Late Pleistocene human remains from East Asia that are reasonably well published are poorly preserved and often have equivocal dates. Since the time the Upper Cave was excavated it has been supposed that the human remains were the link between “Peking Man” and the modern Mongoloid complex. We have carried out multivariate analyses of the “Old Man” cranium employing new measurements of Weidenreich's cast of the skull and comparative data from Howells' survey of modern human groups. Despite our expectations the analyses have not shown the “Old Man” to be closely linked with the Mongoloids. Considering all the evidence available we conclude that the common belief of a close biological relationship between the people buried in the Upper Cave and the modern Mongoloids is not yet adequately demonstrated. Of crucial importance in interpreting the Upper Cave burials is their antiquity, which is still commonly thought to be in the order of at least 18 000 years. We believe that recent C-14 dates of about 11 000 years, determined from animal bones, indicate the earliest possible date for the burials. The time span between the Upper Cave burials and the earliest known modern Mongoloids in north China is in the order of about 4–5000 years. It is possible that a major population shift has occurred in north China between the terminal Pleistocene and the mid Holocene, when farming first appears. If this is so, the Upper Cave people may not have been closely allied to the Mongoloid groups that now inhabit East Asia and the Americas.     

The γ-crystallin gene families: Sequence and evolutionary patterns

Summary The -crystallin proteins consist of two topologically equivalent domains, each built up out of two similar motifs. They are encoded by a gene family, which already contained five members before the divergence of rodents and primates. A further gene duplication took place in each lineage. To analyze the pattern of evolution within this gene family, the coding sequences of six human genes, six rat genes, and four mouse genes were compared. Between species, a uniform rate of evolution of all regions of the protein is seen. The ratio of synonymous to nonsynonymous substitution in the human/rat or human/mouse comparison is much lower than the ratio when rat and mouse are compared indicating that the -crystallin proteins are better conserved in the rodent lineage. Within species, the regions encoding the two external motifs I and III of the protein show a greater extent of nonsynonymous substitution than the regions encoding the two internal protein motifs II and IV. The low extent of synonymous substitution between the second exons (encoding motifs I and II) of the rat -crystallin genes suggests the frequent occurrence of gene conversion. In contrast, a high extent of synonymous substitution is found in exon 3 (encoding motifs III and IV) of the rat genes. The same phenomenon is seen within the human gene family. The frequencies of occurrence of the various dinucleotides deviate less from those predicted from the frequencies of occurrence of each individual nucleotide in the second exons than in the third exons. The sequences of the third exons are significantly depleted in CpG, ApA, and GpT and enriched in CpT and GpA.