Activity of pentose phosphate pathway enzymes in alkane-oxidizing yeast cells]

The activity of the key enzymes of the pentose phosphate pathway (glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, transketolase) was determined in cell-free homogenates of Candida lipolytica 695 and Candida tropicalis 303 growing on different carbon sources. The activity of these enzymes remained almost the same in the course of growth of both cultures. The activity of the enzymes differed only slightly in the cells metabolizing hexadecane and glucose. The activity of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in the cell-free homogenates of C. tropicalis 303 was twice as high as in the cells of C. lipolytica 695. The activity of transketolase was the same in both cultures. The main role of the pentose phosphate pathway is presumed to consist not in catabolism of the carbon source, but in biosynthesis of pentoses and other important intermediates.     

Biochemical Characterization of the Yeast Yarrowia lipolytica Overproducing Carboxylic Acids from Ethanol: Nitrogen Metabolism Enzymes

A comparative assay of nitrogen metabolism enzymes in the Yarrowia lipolytica mutant N1 grown under conditions promoting the overproduction of either -ketoglutaric acid (KGA) or citric acid showed that the overproduction of KGA correlates with an increase in the activities of the NAD- and NADP-linked glutamate dehydrogenase, glutamic–pyruvic transaminase, and glutamic–oxaloacetic transaminase reactions. These reactions are likely to be responsible for the overproduction of KGA by this mutant. In contrast, the overproduction of citric acid correlated with a decline in the activities of the NAD- and NADP-linked glutamate dehydrogenases and with an increase in the activities of glutamine synthetase and glutamate synthase.     

The isolation, purification, and some properties of NAD-dependent isocitrate dehydrogenase from the organic acid-producing yeast Yarrowia lipolytica

The NAD+-dependent isocitrate dehydrogenase of the organic acid-producing yeast Yarrowia lipolytica was isolated, purified, and partially characterized. The purification procedure included four steps: ammonium sulfate precipitation, acid precipitation, hydrophobic chromatography, and gel-filtration chromatography. The enzyme was purified 129-fold with a yield of 31% and had a specific activity of 22 U/mg protein. The molecular mass of the enzyme was found to be 412 kDa. The enzyme consists of eight identical subunits with a molecular mass of about 52 kDa. The Km for NAD+ is 136 microM, and that for isocitrate is 581 microM. The effect of some intermediates of the citric acid cycle and nucleotides on the enzyme activity was studied. The role of isocitrate dehydrogenase (NAD+) in the overproduction of citric and keto acids is discussed.     

Synthesis of acridine derivatives of amino acid hydrazines and their antimalarial activity

2-Methoxy-6-chloroacridine-9-yl- and 2-ethoxy-6-nitroacridine-9-yl-hydrazides of glycine, alpha- and beta-alanines, gamma-aminobutiric acid, epsilon-aminocaproic acid have been synthesized and their antimalarial activity has been investigated. The compounds were found to inhibit the growth of malaria parasite P. falciparum in in vitro cultures. Fifty per cent inhibitory concentrations ranged from 2 x 10(-7) to 6 x 10(-7) M and corresponded to therapeutic concentrations of known quinoline and acridine antimalarial drugs. The beta-alanine and gamma-aminobutiric acid derivatives were the most active and showed high activity against a chloroquine resistant strain of P. falciparum.     

A Spectrophotometric Method for Estimation of the Size and Concentration of Laser Ablated Gold Nanoparticles

Biophysics - Abstract—The ability to use a spectrophotometric method to estimate the size and concentration of gold nanoparticles obtained by the method of laser ablation was considered. Gold...     

Morphology of some species of the genus Aulodrilus Bretscher

The external and internal morphology of Aulodrilus limnobius Bretscher, 1899, Aulodrilus pluriseta (Piguet, 1906) and Aulodrilus japonicus Yamaguchi, 1953, and morphology of the setal apparatus of Aulodrilus pigueti were studied on new material from Russia and compared with various literature data. Besides the peculiar wings on bifid setae, dominance of asexual reproduction is regarded as a primary synapomorphy of the genus and is accompanied by an anterior shift of the whole reproductive system and a tendency to doubling the gonads. Naidid-like cocoons, with a single egg, are another element of this reproductive mode. Similar characters seem to have arisen independently in several groups of Oligochaeta.     

Biosynthesis of citric and isocitric acids by the wild-type and mutant strains of Candida lipolytica in media containing different carbon sources

Experiments were carried out to examine the capacity of two strains of Candida lipolytica, producing citric and isocitric acids in the alkane and glucose containing media, to grow on different two- and three-carbon compounds. The strains did not grow on oxalate, glyoxalate, glycolate, malonate or propionate. When cultivated in the media containing acetate, ethanol, glycerol, glucose or hexadecane, supersynthesis of the acids started after complete consumption of the nitrogen source and resultant delay of the culture growth. Either strain discharged the two acids in a proportion that depended on the strain nature and the type of the carbon source. The mutant strain produced only citrate while the wild-type synthesized both citrate and isocitrate, the ratio of which was related to the nature of the carbon source utilized.     

Regulation of NAD<Superscript>+</Superscript>-dependent isocitrate dehydrogenase in the citrate producing yeast <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis>

The mechanism of the increased accumulation (overproduction) of citric acids in the yeast Yarrowia lipolytica while growing in the presence of glucose under nitrogen deficiency was investigated. The limitation of the yeast growth by the source of nitrogen decreases the total content of nucleotides and increases the ratios of ATP/AMP and NADH/NAD⁺. NAD⁺-Dependent isocitrate dehydrogenase, an enzyme of the tricarboxylic acid cycle playing a key role in the regulation of biosynthesis of citric and isocitric acids, was isolated from Y. lipolytica. The molecular weights of the native enzyme and its subunits were found to be 412 and 52 kD, respectively. It is concluded that the enzyme is a homooligomer consisting of eight subunits. Investigation of the effect of some intermediates of the tricarboxylic acid cycle on the activity of this enzyme suggests that the enhanced excretion of citric acids can be caused by the inhibition of NAD⁺-dependent isocitrate dehydrogenase due to the decrease in the content of AMP and increase in the NADH/NAD⁺ ratio in the cells of Y. lipolytica under depletion of nitrogen.Translated from Biokhimiya, Vol. 69, No. 12, 2004, pp. 1706–1714.Original Russian Text Copyright © 2004 by Morgunov, Solodovnikova, Sharyshev, Kamzolova, Finogenova.     

Grafting of polylysine with polyethylenoxide prevents demixing of O-pyromellitylgramicidin in lipid membranes

Both natural and synthetic polycations can induce demixing of negatively charged components in artificial and possibly in natural membranes. This process can result in formation of clusters (binding of several components to a polycation chain) and/or domains (aggregation of clusters and formation of a separate phase enriched in some particular component). In order to distinguish between these two phenomena, a model lipid membrane system containing ion channels, formed by a negatively charged peptide, O-pyromellitylgramicidin, and polycations of different structures was used. Microelectrophoresis of liposomes, changes in boundary potential of planar bilayers, the shape of compression curves and potentials of lipid and lipid/peptide monolayers were used to monitor the electrostatic factors in polymer adsorption to the membrane and peptide-polymer interactions. The synthesized PEO-grafted polylysine, PLL-PEO20000, did not induce peptide demixing monitored by stabilization of the gramicidin channels, in contrast to parent polylysine (PLL). Both polymers were shown to bind effectively to negatively charged liposomes and lipid monolayers, suggesting that the ineffectiveness of PLL-PEO20000 was not due to reduction of its binding. It was hypothesized that PLL-PEO20000 could not induce domain formation due to steric hindrance of long PEO chains preventing lateral fusion of clusters. Another copolymer, PLL-PEO4000, having four PEO chains of 4000 Da, exhibited intermediate effect between PLL and PLL-PEO20000, which shows the importance of the copolymer architecture for the effect on the lateral distribution of OPg channels. The model system can be relevant to regulation of lateral organization of ion channels and other components in natural membrane systems.