Thermodynamic stability of the ordered conformations of carrageenan polyelectrolytes

Manning's counterion condensation theory has been applied to the temperature-induced conformational transition of κ- and ι-carrageenan in the solution and gel states. The formalism of the theory has been extended to transitions between conformations with charge densities below or across the counterion condensation threshold. Measurements of the dependence of the melting temperature on ionic strength, and of the enthalpy of melting, are interpreted with the theory as indicating that the conformational transition is intramolecular and that side-by-side dimerization of chains gives rise to the gel structure.     

Molecular cut-off values of dialysis membranes for alginate and kappa-carrageenan oligosaccharides

The effective molecular weight cut-off values of dialysis membranes for carrageenan and alginate oligosaccharides were evaluated by gel permeation chromatography and nuclear magnetic resonance spectroscopy. For the different membranes tested, i.e. Medicell, Spectra Por 1000D and 3500D, the porous sizes are analogous to tri- and tetrasaccharides. A simple dialysis can be used to recover the majority of the oligosaccharides produced by a carrageenase or an alginate lyase digestion.     

The use of neocarrabiose oligosaccharides with different length and sulphate substitution as model compounds for 1H-NMR spectroscopy.

The high-field 1H-NMR spectra of various carrageenan oligosaccharides at room temperature are given. The assignments were faciliated by the use of proton double-quantum coherence (DQCOSY) and 1H-13C chemical shift correlation 2D NMR spectroscopy, and by comparing high-field 1H-NMR spectra of various 4-sulphated oligosaccharides of the neocarrabiose type. The effects of anomeric configuration on the 1H resonances on the same or neighbouring units are discussed. The 13C-NMR shift data are given for the tetrasaccharide of kappa-carrageenan.     

31P-NMR studies of phosphate metabolites in intact red and white swimming muscles of cod (Gadus morhua L.)

31P-NMR was used to characterise intracellular phosphate pools and their post mortem changes at 7 degrees C in intact red and white cod muscles under anaerobic conditions. A total phosphate content of 55 and 60 mM was observed in red and white muscle, respectively. The concentration of P-creatine was 14 mM in the white and 9 mM in the red muscle, while that of inorganic phosphate, Pi (30 mM), ATP (9 mM), and sugar phosphate (5 mM) were similar in both muscles. During the first 90 min after death, the decrease in P-creatine showed a first order breakdown with a concomitant stoichiometric increase in Pi content, whereas the ATP and sugar phosphate remained the same. The intracellular pH decreased from 7.4 to 7.3 in this period. The steady-state rate constant of myosin ATPase was 0.0054 and 0.0022/min for red and white muscles, respectively. Individuals kept under diminished oxygen tension prior to being killed, showed a reduced P-creatine level in both muscles.     

Kinetics of hydrolysis of chitin/chitosan oligomers in concentrated hydrochloric acid

The kinetics of hydrolysis in concentrated hydrochloric acid (12.07 M) of the fully N-acetylated chitin tetramer (GlcNAc(4)) and the fully N-deacetylated chitosan tetramer (GlcN(4)) were followed by determining the amounts of the lower DP oligomers as a function of time. A theoretical model was developed to simulate the kinetics of hydrolysis of the three different glycosidic linkages in the tetramers. The model uses two different rate constants for the hydrolysis of the glycosidic bonds in the oligomers, assuming that the glycosidic bond next to one of the end residues are hydrolysed faster than the two other glycosidic linkages. The two rate constants were estimated by fitting model data to experimental results. The results show that the hydrolysis of the tetramers is a nonrandom process as the glycosidic bonds next to one of the end residues are hydrolysed 2.5 and 2.0 times faster as compared to the other glycosidic linkages in the fully N-acetylated and fully N-deacetylated tetramer, respectively. From previous results on other oligomers and the reaction mechanism, it is likely that the glycosidic bond that is hydrolysed fastest is the one next to the nonreducing end. The absolute values for the rate constants for the hydrolysis of the glycosidic linkages in GlcNAc(4) were found to be 50 times higher as compared to the glycosidic linkages in GlcN(4), due to the catalytic role of the N-acetyl group and the presence of the positively charged amino-group on the N-deacetylated sugar residue.     

A new method to estimate the relative bioavailability of individual amino acids in fish larvae using 13C-NMR spectroscopy

In comparison to mammals, fish, and in particular young stages, are thought to have higher amino acid (AA) requirements. Still, little is known about AA requirements of fish larvae, largely due to difficulties in applying traditional methodologies to these fast growing small animals. This study presents a new method to study the qualitative AA requirements of fish larvae. This method combines the use of 13C-labelled live food and 13C-NMR spectroscopy. It allows the simultaneous estimation of the relative bioavailability of several individual AAs. The present study shows that the relative bioavailabilies of various AAs do differ between AAs in larval seabream (Sparus aurata). Threonine has a low relative bioavailability, while aspartate, glutamate and lysine had high relative bioavailabilies compared to other AAs. These results are here attributed to differences in absorption rates by the gut, and/or selective catabolism. The results from the present study suggest that when rotifers are used as the diet for larval seabream, they should be enriched with products rich in threonine and leucine. Information on the relative bioavailability of individual AAs together with the AA profile of the larval protein should allow defining the ideal dietary AA profile for a given species.