Migration of O-acetyl groups in N,O-acetylneuraminic acids

Highly purified N-acetyl-4-O-acetylneuraminic acid (Neu4,5Ac2), N-acetyl-7-O-acetylneuraminic acid (Neu5,7Ac2) and N-acetyl-7,9-di-O-acetylneuraminic acid (Neu5,7,9Ac3) were used to study spontaneous migrations of acetyl groups between hydroxyl groups. The techniques applied involved thin-layer chromatography, gas-liquid chromatography/mass spectrometry, high-performance liquid chromatography and 360-MHz 1H-NMR spectroscopy. It was found that at pH values at which no significant de-O-acetylation is observed: (a) Neu5,7Ac2 can easily be transformed into Neu5,9Ac2, (b) Neu5,7,9Ac3 yields an equilibrium of Neu5,7,9Ac3 and Neu5,8,9Ac3 in a molar ratio of approximately 1:1, and (c) Neu4,5Ac2 does not give rise to O-acetyl migrations. The importance of these findings is discussed in terms of the biosynthesis of O-acetylated sialic acids.     

Stimulation of hepatic glycogenolysis by acetylglyceryl ether phosphorylcholine

1-O-Alkyl-2-acetyl-sn-glyceryl 3-phosphorylcholine or acetylglyceryl ether phosphorylcholine (AGEPC) stimulated glycogenolysis in perfused livers from fed rats at concentrations as low as 10(-11) M. At the lower AGEPC concentrations, e.g. 2 X 10(-10) M, a single transient phase of enhanced hepatic glucose output was elicited upon infusion of this agonist. At higher concentrations, e.g. 2 X 10(-8) M, a sharp transient spike of glucose output was observed, followed by a stable elevated steady state rate of glucose output until the AGEPC infusion was terminated. Increased rates of lactate and acetoacetate output and a diminished hepatic oxygen consumption were characteristic of the response of the livers to AGEPC at 2 X 10(-10) M. Neither alpha- nor beta-adrenergic antagonists blocked the glycogenolytic response of AGEPC. Repeated infusion of AGEPC led to homologous desensitization of the response, but the response of the liver to the alpha-adrenergic agonist, phenylephrine, or to glucagon, subsequent to AGEPC stimulation, was unaffected. Increasing the period of perfusion between successive additions of AGEPC, from 7 to 30 min, resulted in an increased glycogenolytic response to this agonist. When the perfusate calcium concentration was reduced from 1.25 to 0.05 mM, the glycogenolytic response to AGEPC was markedly diminished; calcium efflux from the liver following stimulation with AGEPC was not observed. The data presented in this study illustrate a potent agonist effect of AGEPC on the glycogenolytic system in the rat liver.     

Clinical and experimental keratitis caused by the Colletotrichum state of Glomerella cingulata and Acrophialophora fusispora

Two cases of mycotic keratitis caused by the Colletotrichum state of Glomerella cingulata and Acrophialophora fusispora are reported for the first time. Both the isolates produced experimental corneal lesions in rabbit eyes but A. fusispora was more pathogenic. The experimental infection was more severe, with both the fungi, in rabbits pretreated with cortisone as compared with untreated animals. In vitro A. fusispora was most sensitive to miconazole and tolciclate followed by clotrimazole, amphotericin B and lactones while clotrimazole exerted maximum inhibitory effect on Colletotrichum followed by miconazole, lactones, amphotericin B and arnebins. Arnebins and tolciclate were inactive respectively against A. fusispora and Colletotrichum. Of the 3 drugs tested in vivo, against A. fusispora keratitis in rabbit, amphotericin B showed better results than tolciclate and miconazole.     

Effect of algal hormones on stomatal and epidermal development in rice leaves

Effect of presoaking seeds with different concentrations (0.5, 1 and 5%) of algal extracts on the development of stomata and epidermal cells in rice leaves has been investigated. One percent ether extract of Phormidium foveolarum (Mont.) Gomont suspended in water increases the number of stomata and also the total perimeter of stomatal pores, suggesting that the plants are better adopted for photosynthetic activity.     

Utilization of cuticular components ofAntheraea mylitta Drury larvae byPenicillium citrinum Thom.

The major cuticular components of Indian tasar silkworm,Antheraea mylitta Drury, were sequentially extracted and estimated to ascertain preferential utilization of these components for growth by the entomopathogenic fungusPenicillium citrinum Thom. Proteins which constituted 61.64% dry weight of cuticule were found to play a key role in the growth ofP. citrinum whereas lipids (7.15%) and chitin (30.02%) were least involved. Also, this study suggests absence of any mycocidal substance in the cuticle ofA. mylitta.     

Effects of Iron Limitation on Photosystem II Composition and Light Utilization in Dunaliella tertiolecta

The effects of iron limitation on photosystem II (PSII) composition and photochemical energy conversion efficiency were studied in the unicellular chlorophyte alga Dunaliella tertiolecta. The quantum yield of photochemistry in PSII, inferred from changes in variable fluorescence normalized to the maximum fluorescence yield, was markedly lower in iron-limited cells and increased 3-fold within 20 h following the addition of iron. The decrease in the quantum yield of photochemistry was correlated with increased fluorescence emission from the antenna. In iron-limited cells, flash intensity saturation profiles of variable fluorescence closely followed a cumulative one-hit Poisson model, suggesting that PSII reaction centers are energetically isolated, whereas in iron-replete cells, the slope of the profile was steeper and the calculated probability of energy transfer between reaction centers increased to >0.6. Immunoassays revealed that in iron-limited cells the reaction center proteins, D1, CP43, and CP47, were markedly reduced relative to the peripheral light-harvesting Chl-protein complex of PSII, whereas the [alpha] subunit of cytochrome b559 was about 10-fold higher. Spectroscopic analysis established that the cytochrome b559 peptide did not contain an associated functional heme. We conclude that the photochemical conversion of absorbed excitation energy in iron-limited cells is limited by the number of photochemical traps per unit antenna.