Labile Linker Research Articles

Ocuurrence of polymers containing N-acetylglucosamine-1-phosphate in bacterial walls.

WALLS of Staphylococcus lactis I3 contain substantial proportions of a novel teichoic acid in which N-acetyl-glucosamine l-phosphate residues form an integral part of the polymer chain1,2. A similar teichoic acid is believed3 to be present in walls of Micrococcus hyicus ATCC 11249 and we now report the occurrence of N-acetylglucosamine l-phosphate residues in polymers present in the walls of two further species of bacteria. Sugar l-phosphate linkages are found in yeast phosphomannans4 and phospho-galactans5; the suggestion6 that pneumococcal C-substance is a simple polymer of N-acetylgalactosamine l-phosphate has been shown to be unlikely7, although such a linkage is believed to form the point of attachment between the polysaccharide and peptidoglycan components of the wall of Lactobacillus casei8. Polymers containing such linkages have a characteristically high liability to acid and, in some cases, to alkali; consequently, their distribution may be more widespread than present reports suggest, for the conditions employed for the isolation of polysaccharides would in many cases cause considerable degradation of such comparatively labile linkages.

Action of Heat on Cow κ-Casein. Heat Caseino-Glycopeptide

The main casein components were somewhat degraded when sterilized. The hydrolytic action of heat is not the same as that of rennin. However, for κ-casein, the actions of rennin and of heat (120 C—20min) seem to be similar. A heat caseino-glycopeptide was isolated and it had nearly the same amino acid composition as the rennin caseino-glycopeptide. These data again suggest the existence of a very labile linkage in κ-casein which was easily split by different procedures.

Alkaline labile D-alanine in cell walls.

EVIDENCE has been presented by Baddiley et al.1that “in the native walls the teichoic acid has free phosphate and amino groups and is presumably held in the wall through ionic linkages and hydrogen bonds”. However, Strominger2 has proposed, as an alternative, that the teichoic acid may be “attached to the glycopeptide through the peptide”. In this latter proposal the ester-linked D-alanine of the teichoic acid and the last peptide linked D-alanine of the mucopeptide would be the same alanine residue. Such a linkage would require that cold 5 or 10 per cent trichloroacetic acid, which has been used to remove teichoic acid from walls1, selectively hydrolyses the D-alanyl–D-alanine peptide bond, leaving the other peptide bonds present and the labile ester linkage unaffected. In addition, similarities in the molar ratios of amino-acids and muramic acid in cell walls and in the principal uridine nucleotide (Park compound) which accumulates under conditions of penicillin treatment of Staphylococcus aureus have been used in support of the role of this uridine muramic acid pentapeptide as a direct or nearly immediate precursor of the muramic acid peptide (mucopeptide) of the wall3.

Pools, confluxes and transport of amino acids in Streptococcus faecium

1.1. In OH−-dependent, reversed amino acid transport in Streptococcus faecium it is possible to distinguish the involvement of four confluxes, i.e., groups of amino acids which are released in synchrony from the cell by either a tert.-butanol-isopropanol mixture, trichloroacetic acid, spermine, NH2OH, or OH−.2.2. Conflux 1 (released by the solvent mixture) represents the cell's capacity for concentrative amino acid accumulation; Conflux 2 (released by OH− or spermine without acyl-oxygen bond cleavage) originates from ion-exchanging sites which are key intermediates in reversed transport connected to the loci of Conflux 1 and probably also to sites of both cell wall and protein synthesis; Conflux 3 (released by trichloroacetic acid after a prior extraction with the solvent mixture) containing alanine, lysine, and some peptides, is of unknown relationship to the other confluxes; Conflux 4 (released by NH2OH or OH− with acyl-oxygen bond fission) consisting primarily of aspartic acid, but also containing some leucine, indicates the existence of an unusual, labile, aspartic acyl complex in the cell periphery. However, with regard to Conflux 4, dilute NH4OH, which releases alanine as the amide from a labile linkage in the teichoic acids, did not release leucine amide or isoasparagine in these experiments, although it strongly promoted reserved transport.3.3. The confluxes are compared with the internal and expandable amino acid pools reported in other organisms, and the implications of the heterogeneous metabolic origins and destinations of the confluxes for interpreting the physiological functions of the pools are discussed.

Applications of infrared spectroscopy—IX: The differentiation of esters and acetals from ethers in the zeisel alkoxyl reaction

After determination of the total alkoxyl content (ester + ether groups) by reflux with hydriodic acid, the contribution from methyl and ethyl ester groups is found by refluxing a second sample of the compound in constant-boiling hydrochloric acid for 3 hr. Acetals cannot be distinguished from esters; the yields of alkyl chloride from propyl and butyl esters are diagnostic, although not quantitative. Certain classes of compounds, which have unusually labile ether linkages, restrict the general applicability of the method; examples of such compounds are given.

Radiation Effects on Aqueous Thiourea Solutions

Thiourea and elemental sulfur (1), as well as other compounds containing sulfur in labile organic and inorganic linkage, play an important part in radiation chemical reactions in vitro and in vivo (2-5), owing to their protective action against radiation effects. The protective power of a substance in aqueous solution means its ability to decrease or abolish the effect of radiation on another solute, and this depends on the relative probabilities with which the two substances eliminate radicals formed from the solvent (water) by radiation. Very low concentrations of solute decrease the probability of collision between solute and radicals and therefore favor the recombination of radicals. At higher concentrations of solute this competing recombination gradually becomes negligible; i.e., the radiation yield increases. For some substances a constant yield is reached; for others the yield continuously increases with concentration. This variation in concentration dependence is not yet fully understood, as pointed out in previous communications (6-9). A possible explanation is that with good protectors, i.e., good acceptors of radicals, the recombination of radicals will become more negligible at lower concentrations than with inefficient ones, leading to a constant number of molecules changed per 100 ev (G). Other factors, e.g., molecular weight and shape of molecules, in particular in proteins, may be additional causes. It was observed in preliminary experiments that the amounts of sulfur liberated by ionizing radiations from thiourea increased with concentration without reaching a constant value, although this substance is a good protector. Because of this apparent contradiction in the yield/concentration relationship, it seemed of interest to investigate the radiation chemistry of thiourea in greater detail. The results obtained exceeded the initial purpose of the investigation and revealed various interesting and unusual features in the radiation reaction. Since the preliminary experiments were carried out with the crude technique of weighing very small amounts of sulfur, a more quantitative procedure was adopted 35

The nature of some of the linkages in deoxypentose nucleic acids

AbstractKnowledge of the linkages in deoxyribonucleic acids is reviewed and extended. Chromatographic analyses and electrometric titrations on deoxyribonucleic acids isolated from various sources indicate a greater degree of branching than has been previously assumed. Available evidence on the nature of hydrogen bonding in these nucleic acids is surveyed. Evidence for the possible existence of a highly labile glycosidic linkage is presented. The action of dilute alkali under mild conditions on deoxyribonucleic acids, as described by Euler & Fono (1948), is reinterpreted.

The effect of heat-denaturation on the base-binding capacity of beef-muscle press-juice

The hydrogen ions absorbed ( ΔB ) on heat-denaturation of dialysed and centrifuged beef press-juice is shown to vary with the pH of denaturation along a smooth curve. The values of ΔB are remarkably constant from sample to sample. The main features of the curve are a positive peak at pH 4·1 with troughs on either side, a plateau extending from pH 6·5 to 8·0, and the assumption of negative values of ΔB from pH 8·5 to 10·5. The curve differs from those of undialysed samples and globulin X preparations. The peaks and troughs bear no direct relation to the isoelectric point or the degree of aggregation. Heat-denaturation results in reduction of buffering capacity in the range pH 3·5 to 5·0, and to a new peak in the buffer curve at pH 6·0 to 7·0. Acid-denaturation at pH 3·60 has a similar but smaller effect. The evidence suggests that imidazole groups are released and terminal carboxyl groups absorbed during denaturation. There is no evidence that other amino groups are released or absorbed. These changes in buffering capacity are unlikely to be due merely to changes in physical configuration, not involving chemical bonds, since they occur whether a true coagulum is formed or not. It is suggested that heat- or acid-denaturation result in a fission of the protein chain at labile linkages involving imidazole, sulphydryl and hydroxyl groups, followed by hydrogen-bond formation between carboxyl and amino groups, to give a new configuration. It is shown that these hypothetical changes would give rise to large shifts in pH, and the apparent release or absorption of hydrogen ions ( ΔB ) in a way similar to the actual results. The marked difference in behaviour of the undialysed samples and globulin X prepara­tions, on the one hand, and the crude myogen fraction on the other, suggests a fundamental difference in structure.

DISTURBANCES IN THE GLYCOLYTIC FERMENT SYSTEM OF SKELETAL MUSCLE

1. In intact rabbit's muscle undergoing rigor mortis changes, all the phosphoric acid in labile combinations, and also some more firmly bound as hexose monophosphate, are set free. When the muscle after death is minced, phosphoric acid is again set free, but it is in part used for esterification, and hexose esters appear which form insoluble calcium salts (diesters). These esters, if present at all in fresh muscle or intact rigor mortis muscle, are only in extremely small amount. In monoiodoacetate poisoned muscle the free orthophosphate, and also that obtained from compounds with labile phosphoryl linkages, are rapidly esterified. Just before rigor sets in, the free orthophosphate is diminished to a greater extent than in any other type of muscle examined. Both forms of ester accumulate, the mono‐ and the di‐ester, the latter remaining at a fairly steady level (20 per cent.). In this muscle, unlike the others, extremely little lactic acid is produced during the rigor.2. Ferment extracts of rigor mortis muscle produce predominant esterification with small lactic acid production, but addition of adenosine triphosphate restores the normal glycolytic power. Similar extracts of monoiodoacetate muscle produce esterification practically alone, and addition of the above nucleotide increases the esterification without restoring glycolysis.3. Inactivated extracts of fresh muscle are readily reactivated by the addition of the natural nucleotide, and, associated with the esterification, there is the normal lactic acid production. Inactivated extracts obtained by prolonged dialysis require the addition of the magnesium ion. The co‐ferment activity of the boiled extract of fresh muscle is proportional to the amount of adenosine triphosphate extracted.4. The co‐ferment activity of the nucleotide derivatives is in the following order:— Adenosine triphosphate (or boiled muscle extract) 〉 adenylic acid 〉 inosine triphosphate 〉 inosinic acid 〉 adenine + ribose phosphate.5. At low temperatures, almost immediately after mixing slightly active ferment extracts and substrate with adenosine or inosine triphosphate, the loosely bound H3PO4 of the nucleotide passes into a new organic combination with a firmer linkage. At this time the orthophosphate value is unaltered, but later this falls, and with the esterification lactic acid production commences.6. When adenylic acid is added to ferment extracts in incubation mixtures it rapidly combines with orthophosphate to form adenosine triphosphate, and then follow the processes of esterification and glycolysis.Rabbit's skeletal muscle was used for all experiments, and the methods employed for analysis were briefly as follows:— 1. Deproteinisation and acid extraction. One part minced muscle mixed with coarse quartz sand, extracted with approximately 3 parts 5 per cent. trichloroacetic acid, filtered and neutralised. 2. Phosphorus estimations by slightly modified FISKE and SUBBAROW's method. 3. Lactic acid by FRIEDEMANN, COTONIO, and SHAFFER method. 4. Nucleotide preparations. The adenosine triphosphate by FISKE and SUBBAROW'S method. The other derivatives as described in text.