The Influence of Phytoplankton Primary Production on the Cycle of Biogenic Elements in the Coastal Waters off Sevastopol,Black Sea

The phytoplankton primary production and the biogenic elements content of the coastal waters off Sevastopol have been studied as a result of 2-year monitoring. It has been found that mineral phosphorus is a key factor of chemical limitation of the production processes. During primary production of organic matter, the habitat conditions for phytoplankton in the photic layer are in accordance with the Le Chatelier–Braun principle of negative feedback.     

Properties of the exo-1,4-beta-xylosidase of Aspergillus niger 15

Properties of exo-1,4-beta-xylosidase from the fungus Aspergillus niger 15 were investigated. The enzyme was homogeneous during gel filtration, electrophoresis in polyacrylamide gel in the presence and absence of Na dodecyl sulfate, ultracentrifugation and isoelectric focusing. The enzyme had a temperature optimum at 70 degrees, pH optimum 3.8-4.0 for p-nitrophenyl-beta-D-xylopyranoside (p-NPX), was stable at pH 3-8, retained its 100% activity for 1 hour at 50 degrees and 42% activity at 60 degrees. Km was 0.23 mM for p-NPX and 0.67 mM for xylobiose. Xylose was a competitive inhibitor of exo-1,4-beta-xylodidase with Ki = 2.9 mM. The enzyme showed a transglycosilase activity. The aminoacid analysis of exo-1,4-beta-xylosidase showed that the enzyme molecule contained predominantly dicarboxylic and hydrophobic amino acids as well as serine. The enzyme contained no carbohydrates. Its activity was inhibited by p-chloromercury benzoate.     

Purification and Characterization of endo-(1→4)-β-xylanase fromGeotrichum candidum 3C

A method of purification of endo-( 1 → 4)-β-xylanase (endoxylanase; EC 3.2.1.8) from the culture liquid ofGeotrichum candidum 3C, grown for three days, is described. The enzyme, purified 23-fold, had a specific activity of 32.6 U per mg protein (yield, 14.4%). Endoxylanase was shown to be homogeneous by SDS-PAGE (molecular weight, 60 to 67 kDa). With carboxymethyl xylan as the substrate, the optimum activity (determined viscosimetrically) was recorded at pH 4.0 (pI 3.4). The enzyme retained stability at pH 3.0-4.5 and 30–45°C for 1 h. With xylan from birch wood, the hydrolytic activity of the enzyme (ability to saccharify the substrate) was maximum at 50°C. In 72 h of exposure to 0.2 mg/ml endoxylanase, the extent of saccharification of xylans from birch wood, rye grain, and wheat straw amounted to 10,12, and 7.7%, respectively. At 0.4 mg/ml, the extent of saccharification of birch wood xylan was as high as 20%. In the case of birch wood xylan, the initial hydrolysis products were xylooligosaccharides with degrees of polymerization in excess of four; the end products were represented by xylobiose, xylotriose, xylose, and acid xylooligosaccharides.     

Reproduction and differentiation of the cells in enchondral osteogenesis

Light and electron-microscopical 3H-thymidine autoradiography was used to study the dynamics of cell populations in the zones of enchondral osteogenesis in a tubular bone. In the early postnatal ontogenesis little differentiated perivascular cells are characterized by the highest proliferative activity in this region; they are considered as a population containing initial forms of the histogenetic sequence (differon) of the stromal fibroblast-like cells including osteoblasts. Differentiation of osteogenic cells from the initial forms to the mature osteoblasts proceeds through a number of successive divisions (1-3 divisions) and is accompanied by a decrease in the proliferative activity due to the increase in the generation time and decrease in the cell proliferative pool. The major part of osteoblasts is outside the mitotic cycle. At the later stages of ontogenesis the intensity of growth processes in the bone is provided for by changes in the proliferative pool of the committed precursor cells (preosteoblasts) which make a part of endosteum, vascular channels and bone marrow stroma.     

Fractionation and purification of endo-1,4-beta-xylanases and exo-1,4-beta-xylosidases of Aspergillus niger]

Two endo-1,4-beta-zylanases (m. w. 24,000 and 41,000) and six exo-1,4-beta-xylosidases, differing in their molecular weights and isoelectric points, were found in a xylanase preparation from Aspergillus niger, using different methods of fractionation. An electrophoretically homogeneous exo-1,4-beta-xylosidase (m. w. 30,000) purified 120-fold, with pI 4.6, having optimal effect on methyl-beta-D-xyloside at pH 3.0 was obtained. Exo-1,4-beta-xylosidase splits off xylose from the ends of the xylan chains at xylotriose, xylobiose and methyl-beta-D-xyloside and is characterized by a high transglycosilase activity. An electrophoretically homogeneous endo-1,4-beta-xylanase (m. w. 24,000) purified 250-fold, with pI 4.2 and optimal effect on carboxymethylxylan at pH 4.2 was isolated. Endo-1,4-beta-xylanase splits arabinoglucuronoxylan to form xylooligosaccharides; however, it does not hydrolyze xylobiose.     

beta-Glucosidases from fungus Geotrichum candidum]

beta-Glucosidases from Geotrichum candidum 3C cellulase preparation were separated from C1 enzymes and beta-1,4-glucanases by means of DEAE-Sephadex A-50 chromatography, gel filtration through P-150 Biogel and chromatography on CM-cellulose, and then were fractionated by isoelectric focusing using carrier ampholites with pH ranges 3-6 and 4-6. beta-Glucosidases with pI 3.8, 4.2, 4.6, 5.1, 5.6 and 6.2 were found in cellulase preparation from G. candidum 3C. Molecular weight of beta-glucosidases with pI 3.8, 4.2, 4.6 and 6.2, isolated under isoelectric focusing, were estimated by means of gel filtration through Sephadex G-200 to be 35000, 123000, 188000 and 223000 respectively. beta-Glucosidases with pI 3.8, 4.6, 5.6 and 6.2 hydrolyzed cellobiose and did not attack p-nitrophenyl-beta-D-glucopyranoside; those with pI 4.2 and 5.6 hydrolyzed p-nitrophenyl-beta-D-glucopyranoside and plant glucoside, protodioscin, and did not split cellobiose. All the beta-glucosidases studied did not hydrolyze laminaribose, beta-D-methylsylopyranoside, alder O-methylglucuronoxylane, o-nitrophenyl-beta-D-galactopyranoside and p-nitrophenyl-alpha-D-glucopyranoside. beta-Cellobiase with pI 6.2 hydrolzed lactoses, cellobioses with pI 3.8 and pI 5.6 splited gentiobiose. beta-Glucosidase with pI 4.6 did not attack any substrate studied, except cellobiose.