Muscle fiber types in tetrapods. A comparative histochemical and morphometric study

A comparative histochemical and morphometric study in two groups of homologous muscles from different tetrapods (rat, pigeon, lizard and frog) was performed. On the basis of their fiber diameters and oxidative enzyme activities, an initial correlation between fiber types of all animals is observed, although in the lizard and frog muscles, another fiber type does exists that could not be demonstrated in higher vertebrates. When more than one histochemical techniques are used for the identification of each tetrapod fiber types, the lack of correlation between them becomes obvious. Thus, different animals groups, each showing a characteristic muscle metabolic pattern, could be distinguished.     

Kinetics of alpha-dicarbonyls reduction by L-glycol dehydrogenase from hen muscle

Michaelis constants of L-glycol dehydrogenase from hen muscle (isozyme of pI 7.2) for the alpha-dicarbonyls tested (glyoxal, 2,3-pentanedione, methylglyoxal, and diacetyl) range from 35 microM for pentanedione to 0.41 mM for glyoxal. The enzyme shows a high affinity for NADPH, Km (2.2-3.1 microM), and Ks (1.2-1.9 microM) being so much lower than its tissue concentration that L-glycol dehydrogenase has to operate in vivo saturated with the coenzyme; this condition is very unfavorable to play a role in regulating the equilibrium oxidized/reduced forms of the pyridine nucleotides, as it has been proposed for some similar enzymes. Convergence of the double reciprocal plots and the pattern of inhibition by products and by acetone, a substrate analog, demonstrate that glyoxal reduction--and most likely that of diacetyl--proceeds via an ordered Bi-Bi mechanism in which NADPH is fixed before the addition of the carbonyl; the reduction of methylglyoxal and 2,3-pentanedione could follow the same model, but our experimental results are also consistent with that of Theorell-Chance.     

Processes that drive the population structuring of Jenynsia lineata (Cyprinidontiformes,Anablepidae) in the La Plata Basin

1. The distribution of genetic diversity across a species distribution range is rarely homogeneous, as the genetic structure among populations is related to the degree of isolation among them, such as isolation by distance, isolation by barrier, and isolation by environment.
2. Jenynsia lineata is a small viviparous fish that inhabits a wide range of habitats in South America. To decipher the isolation processes that drive population structuring in J. lineata, we analyzed 221 sequences of the mitochondrial cytochrome c oxidase I gene (COI), from 19 localities. Then, we examined the influence of the three most common types of isolation in order to explain the genetic variation found in this species.
3. Our results revealed a marked structuration, with three groups: (a) La Plata/Desaguadero Rivers (sampling sites across Argentina, Uruguay, and Southern Brazil), (b) Central Argentina, and (c) Northern Argentina. A distance‐based redundancy analysis, including the explanatory variables geographical distances, altitude, latitude, and basin, was able to explain up to 65% of the genetic structure. A variance partitioning analysis showed that the two most important variables underlying the structuration in J. lineata were altitude (isolation by environment) and type of basin (isolation by barrier).
4. Our results show that in this species, the processes of population diversification are complex and are not limited to a single mechanism. The processes that play a prominent role in this study could explain the high rate of diversity that characterizes freshwater fish species. And these processes in turn are the basis for possible speciation events.

     

Effect of gossypol on trypomastigotes and amastigotes of Trypanosoma cruzi

Bloodstream Trypanosoma cruzi trypomastigotes isolated from infected mice undergo reduction of motility and structural damages after 5 to 45 min exposure to gossypol at concentrations ranging from 5 to 50 microM. When 1% serum albumin is added to the incubation medium, no alterations of parasites are observed, even with 100 microM gossypol. Intracellular T. cruzi amastigotes in infected Vero cell cultures exposed to 5 microM gossypol for 2 h do not show changes. Incubation with 5 microM gossypol for 48 h produces complete disruption of host cells; however, the amastigotes they contain show only minor alterations. The observations indicate that, in protein-rich media, gossypol is complexed into associations which have no activity on the different forms of the T. cruzi biological cycle.     

Influence of protein content of diet on growth and lipid composition of European eel muscle and liver

The influence of diet protein content (35-45-55%) on growth and lipid composition of muscle and liver of European eel (Anguilla anguilla) was studied for the first time. In control eel, triacylglycerols constituted about 90% of total lipids in muscle and about 40% in liver. Triacylglycerol content in eel muscle significantly increased after two months of treatment with any diet assayed, with independence of protein content and source. In liver, this increase was comparatively higher in herring meal diets. Total phospholipid content in both muscle and liver drastically decreased after one month of all the experimental treatments, although some recuperation was found at the second month. No significant differences in lipid composition of muscle eel were found among the various experimental groups, in spite of the differences observed in the body weight gain.     

Some notes on the terminology of brassinosteroids

In this paper the definitions of brassinolide, brassinolide activity andbrassins are reviewed, and definitions for the terms brassin, naturalbrassinosteroids and brassinosteroid analogues, based on biosynthetic reasoningand structure similarity are proposed.