2,292 research outputs found
Specificity and kinetics of the milk-clotting enzyme from cardoon (Cynara cardunculus L.) toward bovine .kappa.-casein
The action of Cynara cardunculus L. protease on whole bovine K-casein, over a 3-h period at pH 6.4,
was investigated. RpHPLC of the 3% trichloroacetic acid (TCA)-solublefraction of the K-casein digestion
mixture showed three peptide peaks, which were identified by amino acid analysis and N-terminal
analysis as the 106-169 fragment [caseinomacropeptide (CMP)]. Upon selective precipitation with
12% TCA, one glycosylated and two nonglycosylated forms of CMP were distinguished. Analysis of
the whole digestion mixture showed no additional peptides. The kinetics of hydrolysis of the PhelO5-
Met106 bond was studied by spectrofluorometry, using fluorescein isothiocyanate-labeled K-casein (FTC-
K-casein). The values obtained for kat, k, and k were 1.04 s-l, 0.16 pM, and 6.5 pM-l s-l, respectively.
The proteolytic coefficient is of the same order of magnitude as those obtained for other milk-clotting
enzymes, but the k, is significantly lower, which reflects the higher affinity of Cynara protease to
K-casei
Anomalous dynamics in two- and three- dimensional Heisenberg-Mattis spin glasses
We investigate the spectral and localization properties of unmagnetized
Heisenberg-Mattis spin glasses, in space dimensionalities and 3, at T=0.
We use numerical transfer-matrix methods combined with finite-size scaling to
calculate Lyapunov exponents, and eigenvalue-counting theorems, coupled with
Gaussian elimination algorithms, to evaluate densities of states. In we
find that all states are localized, with the localization length diverging as
, as energy . Logarithmic corrections to density of
states behave in accordance with theoretical predictions. In the
density-of-states dependence on energy is the same as for spin waves in pure
antiferromagnets, again in agreement with theoretical predictions, though the
corresponding amplitudes differ.Comment: RevTeX4, 9 pages, 9 .eps figure
On weak vs. strong universality in the two-dimensional random-bond Ising ferromagnet
We address the issue of universality in two-dimensional disordered Ising
systems, by considering long, finite-width strips of ferromagnetic Ising spins
with randomly distributed couplings. We calculate the free energy and spin-spin
correlation functions (from which averaged correlation lengths, ,
are computed) by transfer-matrix methods. An {\it ansatz} for the
size-dependence of logarithmic corrections to is proposed. Data for
both random-bond and site-diluted systems show that pure system behaviour (with
) is recovered if these corrections are incorporated, discarding the
weak--universality scenario.Comment: RevTeX code, 4 pages plus 2 Postscript figures; to appear in Physical
Review B Rapid Communication
Development of solid-phase extraction for triazines: application to a biological sample.
A sensitive extraction method for the triazines simazine, atrazine, and ametryn was developed and applied to a biological sample (urine). After protein precipitation with acetonitrile, a further purification using solid-phase extraction (SPE) was carried out. The samples were then analysed by high performance liquid chromatography (HPLC) usina a C18 column and an acetonitrile-water (40:60, v/v) mobile phase. The pH of the mobile phase was adjusted to 9.0 with NH4OH, the flow-rate was 0.5 mL/min and UV detection was at 220 nm. Recovery values were satisfactory and the method developed can be used for monitoring urine samples of workers exposed to simazine, atrazine, and ametryn, in forensic, veterinay, and environmental toxicologies
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