Effects of acute handling stress on cerebral monoaminergic neurotransmitters in juvenile Senegalese sole Solea senegalensis.

Juvenile Senegalese sole Solea senegalensis were subjected for short periods to two different types of handling-related stress: air exposure stress and net handling stress. The S. senegalensis were sacrificed 2 and 24 h after the stress events and the levels of serotonin (5-HT), noradrenaline (NA), dopamine (DA) and their respective major metabolites, 5-hydroxyindoleacetic acid (5-HIAA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylacetic acid (DOPAC), were measured in three brain regions (telencephalon, hypothalamus and optic tectum) and compared with those in control, non-stressed S. senegalensis. Neither type of stress caused any significant alteration of serotoninergic activity (5-HIAA:5-HT ratio) or NA levels. Dopaminergic activity (DOPAC:DA ratio) was lower in stressed fish in all of the brain regions studied. For both air exposure stress and net handling stress, DA levels were significantly higher (P < 0.05) than in the control S. senegalensis. In addition, the higher DA levels after net handling stress were always significantly higher (P < 0.05) than those observed after acute air exposure stress, except in the telencephalon after 24 h. The significantly lower DOPAC:DA ratio (P < 0.05) in all of the brain regions studied was only observed in response to net handling stress.

Caffeine inhibition of glycogen phosphorylase from Mytilus galloprovincialis mantle tissue.

A different caffeine inhibition of both phosphorylated and unphosphorylated forms of glycogen phosphorylase from Mytilus mantle has been demonstrated. Caffeine increases the allosteric constant of phosphorylase b 30-fold, acting as an allosteric inhibitor (nH = 2) of mixed type with respect to inorganic phosphate (Pi) and AMP, and of single competitive type with respect to glycogen. The Mytilus phosphorylated form is also caffeine inhibited through competitive inhibition in relation to Pi and glycogen. In this case, the inhibitor does not modify the allosteric constant (near 2), neither does it display allosteric effects (nH = 1). The results demonstrate the notable modification of the nucleotide site promoted by the phosphorylation process and the existence of a functional inhibitory nucleoside site in Mytilus phosphorylase.

Modification of kinetic parameters of glycogen phosphorylase from mantle tissue of Mytilus galloprovincialis by a phosphorylation mechanism.

Initial rate and affinity studies on mantle Mytilus phosphorylase a were carried out in order to find possible differences in its kinetic properties with respect to phosphorylase b. Phosphorylase a was not stimulated for any AMP concentrations. Michaelis constants (Km) are 0.05 mg/ml glycogen, 1.15 mM inorganic phosphate and 1.50 mM glucose-1-phosphate. The Kms for the substrates, in the direction of glycogen breakdown, are enhanced by non-saturating concentrations of cosubstrate, without reducing the apparent maximum velocity. First order and hyperbolic kinetics and values of the allosteric constant smaller than 2 were observed. These results suggest a catalytic mechanism different to that shown for mantle Mytilus phosphorylase b.

[Possible multienzymatic aggregate with glycolytic activity in the digestive gland of the mussel Mytilus galloprovincialis, Lamarck]. / Posible agregado multienzimático con actividad glucolítica en glándula digestiva de mejillón, Mytilus galloprovincialis, Lamarck.

The possible presence of a glycolytic multienzyme complex in the digestive gland from the mussel, Mytilus galloprovincialis, Lamarck, has been investigated. The digestive gland homogenate was concentrated an applied to a Sepharose-2B column. The elution profile demonstrates that two species of glycolytic enzymes were eluted from the column. Most of the enzyme activity appeared in the low-molecular-weight region, the enzymes being eluted as individual entities in order of their molecular weights. However, a proportion of each enzyme activity was found in the high-molecular-weight region of eluate, with those activities showing a high degree of co-chromatography. By using a column calibrated with a series of marker proteins of known molecular weight, the activity peak for the high-molecular-weight species corresponded to a molecular weight of 3 X 10(6) +/- 10(5) d. Finally, it has been found that a sample of the high-molecular-weight species was able to catalyse the production of piruvate when it was incubated with different glycolytic substrates and the appropriate cofactors.