Deposition of condensed phosphate as an effect of varying sulfur deficiency in the cyanobacterium Synechococcus sp. (Anacystis nidulans)

Uptake of orthophosphate and deposition of condensed phosphate were investigated in cells of Synechococcus sp. (Anacystis nidulans) deficient in phosphorus or sulfur. When phosphorus was restored to phosphorus-starved cells, uptake was rapid and immediate, with the greatest accumulation occurring within the first hour. Uptake was optimum in the pH 7.5–8.5 range. Long-term (6-day) studies of uptake and deposition with cells exposed to a wide range of sulfur deficiency showed that both processes were greatest when the level of exogenous sulfur was reduced to zero. The increase in cellular phosphorus as determined chemically was in agreement with the increased number and size of polyphosphate bodies at the ultrastructural level. Possible mechanisms for the control of phosphorus uptake and condensed phosphate formation by exogenous sulfur are discussed.     

The SGLT2 inhibitor dapagliflozin promotes systemic FFA mobilization,enhances hepatic β-oxidation,and induces ketosis

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have been shown to increase ketone bodies in patients with type 2 diabetes; however, the underlying mechanisms have not been fully elucidated. Here we examined the effect of the SGLT2 inhibitor dapagliflozin (1 mg/kg/day, formulated in a water, PEG400, ethanol, propylene glycol solution, 4 weeks) on lipid metabolism in obese Zucker rats. Fasting FFA metabolism was assessed in the anesthetized state using a [9,10-³H(N)]-palmitic acid tracer by estimating rates of plasma FFA appearance (R_a), whole-body FFA oxidation (R_ox), and nonoxidative disposal (R_st). In the liver, clearance (K_β-ox) and flux (R_β-ox) of FFA into β-oxidation were estimated using [9,10-³H]-(R)-bromopalmitate/[U-¹⁴C]palmitate tracers. As expected, dapagliflozin induced glycosuria and a robust antidiabetic effect; treatment reduced fasting plasma glucose and insulin, lowered glycated hemoglobin, and increased pancreatic insulin content compared with vehicle controls. Dapagliflozin also increased plasma FFA, R_a, R_ox, and R_st with enhanced channeling toward oxidation versus storage. In the liver, there was also enhanced channeling of FFA to β-oxidation, with increased K_β-ox, R_β-ox and tissue acetyl-CoA, compared with controls. Finally, dapagliflozin increased hepatic HMG-CoA and plasma β-hydroxybutyrate, consistent with a specific enhancement of ketogenesis. Since ketogenesis has not been directly measured, we cannot exclude an additional contribution of impaired ketone body clearance to the ketosis. In conclusion, this study provides evidence that the dapagliflozin-induced increase in plasma ketone bodies is driven by the combined action of FFA mobilization from adipose tissue and diversion of hepatic FFA toward β-oxidation.     

Woronin bodies in arthrinium genus

Woronin bodies are present near all septal pores and in conidia of Arthrinium strains and may regulate cytoplasmic flow in both injured and actively growing healthy colonies. They vary in size and frequency, the central one plugs the septal pores in actively developing colonies and in mature conidia. The septa are thinner in the Woronin-body region.     

Isolation of legumin-like protein from Phaseolus aureus and Phaseolus vulgaris

An 11S seed globulin has been isolated from Phaseolus aureus and P. vulgaris by zonal isoelectric precipitation and the MWs of the constituent subunits determined. The protein of P. vulgaris occurs in the protein body fraction and its chemical composition, including the N-terminal amino acids and amino acid composition has been determined. The similarity between the 11S globulin of the two Phaseolus spp. and legumin from other leguines is discussed.     

The coiled-coil domain of Escherichia coli FtsLB is a structurally detuned element critical for modulating its activation in bacterial cell division

The FtsLB complex is a key regulator of bacterial cell division, existing in either an off state or an on state, which supports the activation of septal peptidoglycan synthesis. In Escherichia coli, residues known to be critical for this activation are located in a region near the C-terminal end of the periplasmic coiled-coil domain of FtsLB, raising questions about the precise role of this conserved domain in the activation mechanism. Here, we investigate an unusual cluster of polar amino acids found within the core of the FtsLB coiled coil. We hypothesized that these amino acids likely reduce the structural stability of the domain and thus may be important for governing conformational changes. We found that mutating these positions to hydrophobic residues increased the thermal stability of FtsLB but caused cell division defects, suggesting that the coiled-coil domain is a “detuned” structural element. In addition, we identified suppressor mutations within the polar cluster, indicating that the precise identity of the polar amino acids is important for fine-tuning the structural balance between the off and on states. We propose a revised structural model of the tetrameric FtsLB (named the “Y-model”) in which the periplasmic domain splits into a pair of coiled-coil branches. In this configuration, the hydrophilic terminal moieties of the polar amino acids remain more favorably exposed to water than in the original four-helix bundle model (“I-model”). We propose that a shift in this architecture, dependent on its marginal stability, is involved in activating the FtsLB complex and triggering septal cell wall reconstruction.     

Purine-Excretory Nature of Refractile Bodies in the Marine Ciliate Parauronema acutum*

SYNOPSIS. A method was developed for the isolation and purification of crystalline, highly refractile bodies found in the cytoplasm of a symbiote-free strain of the marine hymenostome ciliate, Parauronema acutum, strain 110–3. Chemical analysis of the purified refractile bodies revealed an abundance of the purines, hypoxanthine and guanine. It was evident from studies involving the use of ¹⁴C-labeled precursors that both hypoxanthine and guanine are derived from higher purine derivatives. We postulate that these bodies are excretory in function and that guanine and hypoxanthine are major endproducts of purine metabolism of P. acutum.     

At5g50600 encodes a member of the short-chain dehydrogenase reductase superfamily with 11beta- and 17beta-hydroxysteroid dehydrogenase activities associated with Arabidopsis thaliana seed oil bodies

In a previous work, we presented evidence for the presence of a protein encoded by At5g50600 in oil bodies (OBs) from Arabidopsis thaliana [P. Jolivet, E. Roux, S. D'Andrea, M. Davanture, L. Negroni, M. Zivy, T. Chardot, Protein composition of oil bodies in Arabidopsis thaliana ecotype WS, Plant Physiol. Biochem. 42 (2004) 501-509]. Using specific antibodies and proteomic techniques, we presently confirm the existence of this protein, which is a member of the short-chain steroid dehydrogenase reductase superfamily. We have measured its activity toward various steroids (cholesterol, dehydroepiandrosterone, cortisol, corticosterone, estradiol, estrone) and NAD(P)(H), either within purified OBs or as a purified bacterially expressed chimera. Both enzymatic systems (OBs purified from A. thaliana seeds as well as the chimeric enzyme) exhibited hydroxysteroid dehydrogenase (HSD) activity toward estradiol (17beta-hydroxysteroid) with NAD+ or NADP+, NADP+ being the preferred cofactor. Low levels of activity were observed with cortisol or corticosterone (11beta-hydroxysteroids), but neither cholesterol nor DHEA (3beta-hydroxysteroids) were substrates, whatever the cofactor used. Similar activity profiles were found for both enzyme sources. Purified OBs were found to be also able to catalyze estrone reduction (17beta-ketosteroid reductase activity) with NADPH. The enzyme occurring in A. thaliana OBs can be classified as a NADP+-dependent 11beta-,17beta-hydroxysteroid dehydrogenase/17beta-ketosteroid reductase. This enzyme probably corresponds to AtHSD1, which is encoded by At5g50600. However, its physiological role and substrates still remain to be determined.     

Structural characterization of KKT4, an unconventional microtubule-binding kinetochore protein

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