Influence of Organic-Phosphates on 3-Phosphoglycerate Dependent O2 Evolution in C3 and C4 Mesophyll Chloroplasts

In C₄ plants phosphoenolpyruvate (PEP) of the C₄ cycle may betransported on a chloroplast transporter which also transports3-phosphoglycerate (3-PGA) and triosephosphates. In C₃ plantsPEP is not considered to be effectively transported on the chloroplastphosphate translocator. The influences of certain organic phosphates,having a similar structure to either PEP or triose-phosphates,on 3-PGA dependent O₂ evolution by C₄ (Digitaria sanquinalisL. Scop.) and C₃ (Hordeum vulgare L.) mesophyll chloroplastswere investigated. In the C₄ mesophyll chloroplasts phosphoglycolatewas a competitive inhibitor (K_i = 2.1 mM) of 3-PGA dependentO₂ evolution, and was as effective as previously reported forPEP. 2-Phosphoglycerate was also a competitive inhibitor (K_t= 8.6 mM) of O₂ evolution in the C₄ mesophyll chloroplasts with3-PGA as substrate, while phospholactate was a weak inhibitorand glyphosate had no effect. Neither PEP, phosphoglycolatenor 2-phosphoglycerate were effective inhibitors of 3- PGA dependentO₂ evolution in the C₃ chloroplasts. Phosphohydroxypyruvatewas a competitive inhibitor of 3-PGA dependent O₂2 evolutionin both chloroplast types. The selectivity in inhibition ofO₂ evolution with 3-PGA as substrate suggests that the C₄ mesophyllchloroplasts can recognize certain organic phosphates with thephosphate in the C-2 or C-3 position but that the C₄ mesophyllchloroplasts can only effectively recognize certain organicphosphates with the phosphate in the C-3 position. The resultsalso support the view that 3-PGA and PEP are transported onthe same phosphate translocator in C₄ mesophyll chloroplasts. ¹ Current address: Department of Horticulture, 2001 Fyffe Court,The Ohio State University, Columbus, Ohio 43210-1096. (Received March 24, 1987; Accepted April 16, 1987)     

Study on the enzymatic 5′-deiodination of 3′,5′-diiodothyronine using a radioimmunoassay for 3′-iodothyronine

A radioimmunoassay for 3′-iodothyronine has been developed. All iodothyronine analogues (except 3,3′-diiodothyronine) showed very little (0.02% at most) cross-reactivity, and the assay was sensitive to 1 pg 3′-iodothyronine/ tube. We have studied the 5′-deiodination of 3′,5′-diiodothyronine by rat liver microsomal fraction in the presence of dithiothreitol. Production of 3′-iodothyronine at 37°C was found to be linear with time of incubation up to 30 min and with concentration of microsomal protein up to 100 μg/ml. The reaction rate reached a limit on increasing 3′,5′-diiodothyronine concentration to 10 μM. The effect of pH on 3′-iodothyronine production was found to depend on 3′,5′-diiodothyronine concentration. Increasing 3′,5′-diiodothyronine concentration from 0.1 to 10 μM resulted in a shift of the pH optimum from 6–6.5 to 7.5. Similar effects on the 5′-deiodination of 3,3′,5′-triiodothyronine were observed, supporting the hypothesis that these reactions are catalysed by a single enzyme (iodothyronine 5′-deiodinase).     

Phenotypic dissections of the Blastocladiella emersonii zoospore's developmental choice

A developmentally homogeneous neural crest cell population has been used to assay the role of environmental factors in regulating crest cell differentiation. If cultured on tissue culture plastic, virtually all of the cells of this population differentiate into melanocytes. In contrast, when these cells are cultured for 3 or more days on substrata “conditioned” by somite fibroblasts, the proportion of cells undergoing melanogenesis decreased and the proportion expressing formaldehyde-induced fluorescence (FIF), characteristic of catecholamine-containing cells, increased. For a limited period of culture on somite-conditioned substrata, some cells in the population exhibit both pigment granules and fluorescence. Collagen-coated substrata decreased the number of cells that formed pigment but did not stimulate FIF. In contrast, optimum doses of exogenous cellular fibronectin mimicked the effect of somite-conditioned substrata, suppressing melanogenesis and promoting FIF. Glycosaminoglycan-derivatized substrata (i.e., hyaluronic acid, various chondroitin sulfate preparations, and heparin) did not alter the differentiative homogeneity of the cultured crest cell populations. The choice and expression of phenotype by some members of a cultured crest cell population can, therefore, be affected by environmental stimuli provided in the form of certain substrate-attached macromolecules. We suggest that optimal concentrations of some extracellular matrix components produced by embryonic tissue and normally encountered by migrating crest cells may elicit the expression of FIF in crest cells that would otherwise follow a different developmental pathway.     

Transfer and expression of the tetracyclin resistance transposon Tn925 in Acetobacterium woodii

The Enterococcus faecalis conjugative plasmid pCF10 was used to introduce Tn925 into Acetobacterium woodii by filter mating. Tetracycline resistance was transferred at frequencies of about 10(-6) per donor, but no plasmid DNA was found in the transconjugants. DNA hybridization analyses of HindIII-digested chromosomal DNA demonstrated the insertion of Tn925 at a variety of locations, whereas wild type DNA showed no hybridization at all. The transconjugants were used as donor in mating experiments with tetracycline-sensitive Bacillus subtilis. Transfer of tetracycline resistance was observed at frequencies of 10(-8) per recipient.     

Generation of a transmembrane gradient of Na+ in Methanosarcina barkeri

A transmembrane Na+ gradient was generated by Methanosarcina barkeri during methanogenesis. The intracellular Na+ concentration amounted to approximately one fifth of the extracellular one. A secondary Na+/H+ antiport system was shown to be responsible for Na+ extrusion. This system could be inhibited by amiloride. In the presence of amiloride the delta pH across the cytoplasmic membrane increased and a transmembrane Na+ gradient could neither be generated nor maintained. The possible role of Na+ in the oxidation of methanol to the level of formaldehyde is discussed.     

Moral medicine: Symbolic content in 19th century Shaker therapeutics

This paper presents an analysis of the symbolic meanings implicit in an ostensibly empirical therapeutic system. The Shakers, a celibate communal religious order founded in New York State in the mid 1770s, were practitioners of botanic medicine, as were many other Americans in the nineteenth century. This study analyzes the therapeutic properties of the herbs they produced (such as diuretic, stimulant, narcotic, emetic, astringent), using a classification scheme based on the location of the botanical substance's effect vis-à-vis body boundaries and surfaces. The Shakers' beliefs about the therapeutic properties of their herbs are compared with similar analyses of the properties given by two contemporary nineteenth century New England proponents of herbal medicine, botanist Constantine Rafinesque and sectarian practitioner Samuel Thomson. The comparison shows systematic variation in emphasis given to herbs which regulate internal body processes, or act through the openings of the body or on its surface. In this context Shaker medicine can be characterized as quickening, internal, and purifying in its effects on body processes, effects which are highly consistent with Shaker religious beliefs in active, physical worship, selflessness and spiritual purification by confession.