Polysialic acids

• 1.1. Polysialic acids are linear homopolymers of N-acetylneuraminic acid (Neu5Ac), N-glycolylneuraminic acid (Neu5Gc) and deaminated neuraminic acid (KDN) residues joined by α 2,8, α 2–9 or α2,8/α2,9 ketosidic linkages.
• 2.2. They occur in glycoproteins of embryonic neural membranes (playing a role of neural cell adhesion molecules), in non-neural tissues (postnatal kidney), tumours, (neuroectodermal tumours), fish eggs and in the capsule of certain bacteria such as Neisseria meningitidis group B.
• 3.3. These polymers are synthesized through reactions which involve (a) the synthesis of sialic acid; (b) its activation to a cytidine monophosphate sugar nucleotide and (c) the polymerization of the different residues by a polysialyl-transferase complex.
• 4.4. Polysialic acids are involved in organogenesis and in cell growth. In several tissues they act as oneodevelopmental antigens, and in bacteria are also virulent determinants.

     

Intermediates in the metabolism of m-carboxy-substituted aromatic amino acids in plants: Phenylpyruvic acids,mandelic acids,and phenylglyoxylic acids

Tracer experiments with ¹⁴C-labelled precursors in Iris × hollandica cv. Wedgwood, Roseda lutea L. and Reseda Odorata L. have demonstrated that 3-(3-carboxyphenyl)alanine and 3-(3-carboxy-4-hydroxyphenyl)alanine can be derived from the corresponding pyruvic acids, presumably by unspecific trans-aminations, and that (3-carboxyphenyl)glycine and (3-carboxy-4-hydroxy-phenyl)glycine can be derived from the corresponding phenylglyoxylic acids The glycine derivatives are derived from the alanine derivatives, and the corresponding mandelic acids are intermediates in these transformations. The corresponding phenylacetic acids are incorporated only slightly into the glycine derivatives, indicating that oxidation at the benzylic position in the C₆–C₃ compounds takes place early in the transformation. The corresponding cinnamics acids are not metabolized at all in the plants.     

Enzymatic conversion of N carbamoyl-d-amino acids to d-amino acids

An enzyme isolated from Agrobacterium radiobacter was shown to catalyse the following reaction: $\text{H}{}_2\text{O}\text{+ N-}\text{carbamoyl-}\text{d}\text{-amino acid}\text{→}\text{d}\text{-amino acid}\text{+}\text{NH}{}_3\text{+}\text{CO}{}_2$ Some properties of this new enzyme, $\text{N-}\text{carbamoyl-}\text{d}\text{-amino}$ acid amidohydrolase, are presented in this paper. The potential application of this enzyme for the preparation of some d-amino acids used as pharmaceutical intermediates is discussed.     

Microbial desulfonation of substituted naphthalenesulfonic acids and benzenesulfonic acids

Sulfur-limited batch enrichment cultures containing one of nine multisubstituted naphthalenesulfonates and an inoculum from sewage yielded several taxa of bacteria which could quantitatively utilize 19 sulfonated aromatic compounds as the sole sulfur source for growth. Growth yields were about 4 kg of protein per mol of sulfur. Specific degradation rates were about 4 to 14 mu kat/kg of protein. A Pseudomonas sp., an Arthrobacter sp., and an unidentified bacterium were examined. Each desulfonated at least 16 aromatic compounds, none of which served as a carbon source. Pseudomonas sp. strain S-313 converted 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 5-amino-1-naphthalenesulfonic acid, benzenesulfonic acid, and 3-aminobenzenesulfonic acid to 1-naphthol, 2-naphthol, 5-amino-1-naphthol, phenol, and 3-aminophenol, respectively. Experiments with 18O2 showed that the hydroxyl group was derived from molecular oxygen.     

Microbial desulfonation of substituted naphthalenesulfonic acids and benzenesulfonic acids.

Sulfur-limited batch enrichment cultures containing one of nine multisubstituted naphthalenesulfonates and an inoculum from sewage yielded several taxa of bacteria which could quantitatively utilize 19 sulfonated aromatic compounds as the sole sulfur source for growth. Growth yields were about 4 kg of protein per mol of sulfur. Specific degradation rates were about 4 to 14 mu kat/kg of protein. A Pseudomonas sp., an Arthrobacter sp., and an unidentified bacterium were examined. Each desulfonated at least 16 aromatic compounds, none of which served as a carbon source. Pseudomonas sp. strain S-313 converted 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 5-amino-1-naphthalenesulfonic acid, benzenesulfonic acid, and 3-aminobenzenesulfonic acid to 1-naphthol, 2-naphthol, 5-amino-1-naphthol, phenol, and 3-aminophenol, respectively. Experiments with 18O2 showed that the hydroxyl group was derived from molecular oxygen.     

Modeling nucleic acids

Nucleic acids are an important class of biological macromolecules that carry out a variety of cellular roles. For many functions, naturally occurring DNA and RNA molecules need to fold into precise three-dimensional structures. Due to their self-assembling characteristics, nucleic acids have also been widely studied in the field of nanotechnology, and a diverse range of intricate three-dimensional nanostructures have been designed and synthesized. Different physical terms such as base-pairing and stacking interactions, tertiary contacts, electrostatic interactions and entropy all affect nucleic acid folding and structure. Here we review general computational approaches developed to model nucleic acid systems. We focus on four key areas of nucleic acid modeling: molecular representation, potential energy function, degrees of freedom and sampling algorithm. Appropriate choices in each of these key areas in nucleic acid modeling can effectively combine to aid interpretation of experimental data and facilitate prediction of nucleic acid structure.     

Extracellular nucleic acids

Extracellular nucleic acids are found in different biological fluids in the organism and in the environment: DNA is a ubiquitous component of the organic matter pool in the soil and in all marine and freshwater habitats. Data from recent studies strongly suggest that extracellular DNA and RNA play important biological roles in microbial communities and in higher organisms. DNA is an important component of bacterial biofilms and is involved in horizontal gene transfer. In recent years, the circulating extracellular nucleic acids were shown to be associated with some diseases. Attempts are being made to develop noninvasive methods of early tumor diagnostics based on analysis of circulating DNA and RNA. Recent observations demonstrated the possibility of nucleic acids exchange between eukaryotic cells and extracellular space suggesting their participation in so far unidentified biological processes.