Age determination based on amino acid racemization: a new possibility

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Effect of microorganisms on free amino acid and free D-amino acid contents of various dairy products

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Influence of mastitis on D-amino acid content of milk

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Investigation of performic acid oxidation in case of thiol-containing amino acid enantiomers

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SEPARIRANJE I ODREĐIVANJE ENANTIOMERA AMINOKISELINA KOJE SADRŽE SUMPOR POMOĆU TEKUĆE KROMATOGRAFIJE VISOKE PERFORMANCE

Performic acid oxidation of cysteine and methionine resulting in the formation of cysteic acid and methionine sulphon has been applied in order to avoid the loss of these two sulphur containing amino acids during the acidic hydrolysis of proteins that is necessary prior to amino acid analysis. The aim of the research was assigned by the increasing demand for the determination of the amount of amino acid enantiomers: the applicability of performic acid oxidation was evaluated from this point of view. Racemization of L-cysteine and L-methionine was found not significant during oxidation with performic acid, therefore this process can be applied before hydrolysis during quantification of cysteine and methionine enantiomers. Additionally, the quantification of cysteic acid and methionine sulphon enantiomers was accomplished in the form of their diastereoisomer derivatives via the development of a reversed phase of high performance liquid chromatography method.Proces oksidacije performičnom kiselinom cisteina i metionina, što rezultira stvaranjem cisteične kiseline i sulfona metionina primijenjen je kako bi se izbjegao gubitak te dvije aminokiseline koje sadrže sumpor, za vrijeme acidične hidrolize bjelančevina, potrebne prije analize aminokiselina. Cilj istraživanja potakli su sve veći zahtjevi za određivanjem količina enantiomera aminokiselina: primjenjivost oksidacije performične kiseline ocijenjena je s tog gledišta. Racemizacija L-cisteina i L-metionina nije se pokazala značajnom za vrijeme oksidacije s performičnom kiselinom pa se, stoga, taj proces može primijeniti prije hidrolize tijekom kvantifikacije cisteinskih i metioninskih enantiomera. Osim toga, kvantifikacija cisteične kiseline i enantiomera metionskog sulfona izvedena je u obliku derivata njihovih dijastereosomera putem razvoja obrnute faze metode tekuće kromatografije visoke performance

A new method for the quantitative determination of protein of bacterial origin on the basis of D-aspartic acid and D-glutamic acid content

In the past years several methods have been developed for the determination of the proportion of the nitrogen-containing substances of microbial origin passed from the rumen into the abomasum or the small intestine. Recently, on examining the D-amino acid content of foodstuffs, particularly milk and milk products, it has been observed that, in addition to D-Ala, D- glutamic acid (D-Glu) and D-aspartic acid (D-Asp) can also be detected in similar quantities, primarily in products which have links with bacterial activity. This gave rise to the idea of examining the diaminopimelic acid (DAPA), D-Glu and D-Asp content of bacteria extracted from the rumen of cattle and that of chyme from the same cattle, in order to determine the type of relation existing among these three components, and to establish whether D-Asp and D-Glu can be used in the estimation of protein of bacterial origin. On determination of the DAPA, D-Asp and D-Glu content by means of amino acid analyser and high performance liquid chromatography of duodenal chyme from five growing bulls and of ruminal bacteria from the same bulls, the following values were established. For chyme (and, in brackets, for ruminal bacteria) r value calculated by means of linear regression was 0.78 (0.76) between DAPA and D-Asp, and 0.70 (0.81) between DAPA and D-Glu. The r values between the crude protein content of ruminal bacteria and the markers examined were found to be the following: DAPA, 0.74; D-Asp, 0.73; D- Glu, 0.61. In the model experiment performed for the re-obtaining of values for protein of bacterial origin the theoretical values were determined on the basis of D-Asp and D-Glu and values approximately 10% higher than the theoretical value on the basis of DAPA. It is therefore recommended that in addition to DAPA these other two amino acids be included among the bacterial protein markers

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Flow microenvironment of two marine peritrich ciliates with ectobiotic chemoautotrophic bacteria

The flow microenvironment of 2 marine peritrich ciliates, Vorticella sp. and Zoothamnium niveum, with ectobiotic sulfur bacteria was studied with frame-by-frame analyses of video sequences and a microsensor for fluid velocity. Both species populate the chemocline above H2Sreleasing mangrove peat. Vorticella sp. moves the surrounding seawater up to a horizontal and vertical distance of at least 400 μm with a maximum flow velocity of 18 mm s–1 close to its peristomial edge. The feather-shaped colonies of Z. niveum generate a unidirectional flow of seawater passing the colony perpendicular to the stalk; the convex side of the feather faces upstream. The flow velocity increased exponentially towards the colony, up to 11 mm s–1 at a distance of 100 μm. Contraction of the stalk forces the zooids of Vorticella sp. and Z. niveum towards the substrate at a high velocity of 71 and 520 mm s–1, respectively. During contraction of Vorticella sp., only little seawater is dragged along towards the surface to which the ciliates are attached whereas the contraction of Z. niveum resulted in a clear increase in the velocity of the seawater both surrounding the colony and above the substrate. Extension of the species proceeds 700 to 1000 times more slowly than contraction, and the surrounding seawater sticks to the cells and therefore is dragged along. The measurements given here support our earlier data indicating the importance of the feeding current for the bacteria-ciliate association, i.e. the cilia beat drives H2S- and O2-containing seawater toward the zooid at high velocity and thus, supports the growth of the ectobiotic sulfide-oxidizing bacteria. Rapid movement, shrinkage (Vorticella sp.) and bunching (Z. niveum) of the zooids during stalk contraction apparently cause sufficient shear stress to abrade ectobiotic bacteria that, once suspended, could enter the feeding currents