Underwater observations of piranhas in western Brazil

Synopsis The behaviour of three piranha species,Serrasalmus marginatus, S. spilopleura, andPygocentrus nattereri, and their prey fishes was studied underwater in the Pantanal region, Mato Grosso, Brazil. General habits, predatory tactics, feeding behaviour, and social interactions while foraging, as well as defensive tactics of prey fishes were observed.S. marginatus is solitary whereas the other two species live in shoals; their agonistic behaviour varies accordingly, the simplest being displayed by the solitary species. Predatory tactics and feeding behaviour also vary:S. spilopleura shows the most varied diet and highly opportunistic feeding strategy, which includes aggressive mimicry. The solitaryS. marginatus, besides fin and scale-eating, occasionally cleans larger individuals ofP. nattereri. Several cichlid species display defensive tactics clearly related to piranha attacks: tail protecting, watching, and confronting the predator are the most commonly observed behaviours. Piranhas seem to strongly influence use of habitat, social structure, and foraging mode of the fish communities.     

Nonuniform size distribution of nascent globin peptides, evidence for pause localization sites, and a cotranslational protein-folding model

Examination of nascent globin peptides accumulatingin vitro during globin synthesis in rabbit reticulocyte lysates was carried out. A view was supported that nonrandom distribution of codons with different usage frequencies in mRNA may determine the messenger's translation kinetics. Regions of reduced translation of - and -globin polypeptide chains were localized, and the cotranslational protein-folding model suggested previously was substantiated. An active conjunction of synthesis and folding of proteins was proposed as one of the main destinations of a translation nonuniformity.     

The sulphydryl groups of ox brain and liver glutamate dehydrogenase preparations and the effects of oxidation on their inhibitor sensitivities

Glutamate dehydrogenase preparations from several sources have been shown to have suffered limited proteolysis during purification. This proteolysis has been previously shown to involve removal of the N-terminal tetrapeptide and to result in changes in the regulatory properties of the enzyme. In the present work the previously unidentified N-terminal residue of the unproteolysed enzyme from ox brain and liver is shown to be cysteine. The thiol group of this residue is masked in the native enzyme but it becomes accessible after reduction. Exposure of solutions of the unproteolysed enzyme to air oxidation causes large changes in its sensitivity to inhibition by the antipsychotic drug perphenazine, GTP and by high concentrations of NADH. No such changes occurred in the behaviour of preparations of the enzyme that had suffered proteolysis during purification under these conditions.Special issue dedicated to Dr. Santiago Grisolia.     

The effect of H-21J disparity on induction of allotransplantation tolerance by Lentil Lectin

The effect of an H-21J disparity on skin graft survival was studied in 18 mouse donor-recipient strain combinations, in which the recipients were treated with an efficient immunosuppressant, lentil lectin (LCA). The simultaneous I-J disparity essentially had no (or a slightly adverse) effect on the graft survival times in strain combinations differing at the K and I-A loci or in the entire H-2 complex. In two strain combinations incompatible at the D locus, the simultaneous I-J disparity promoted graft survival. The disparity at the I-J locus therefore seems to have only a marginal effect on the survival of allografts in most of the LCA-treated recipients, but it may promote graft survival in some animals. A similar tolerance-promoting effect was also observed with D disparity.     

Analysis of characters coded for by T-DNA using hybridization between tumorous and normal plant cells

In somatic hybrids between tumourous Nicotiana tabacum (B6S3) and normal mesophyll Atropa belladonna cells, the following traits, directly or indirectly connected with T-DNA gene expression and tumourous growth, were analysed: lysopine dehydrogenase activity (LpDH), shoot suppression, root suppression, ability to grow on media with D-lactose as a sole carbon source and resistance to 2-aminoethylcysteine, 5-bromodeoxyuridine and 5-methyltryptophan. Dominant (semidominant) expression was observed for all but one trait studied, e.g. shoot suppression which behaved as a recessive character.Abbreviations LS-H Linsmaier and Skoog (1965) hormone-free medium - NAA Naphtaleneacetic acid - BAP 6-Benzylaminopurine - 2,4-D 2,4-Dichlorophenoxyacetic acid - 5-BUdR 5-Bromodeoxyuridine - 2-AEC 2-Aminoethylcysteine - 5-MT 5-Methyltryptophan     

Unusual genome organization of the marine invertebrate Rapana thomasiana Grosse (Gastropoda)

The genome organization of the marine snail Rapana thomasiana Grosse (Gastropoda), genome size 2.7 pg, was studied by reassociation kinetics, S₁-nuclease assay, and restriction enzyme analysis. The slow-reassociating (single-copy) fraction represented only 21% of the genome. The average length of 80% of the single-copy sequences was less than 700 bp and the remaining 20% no longer than 1,400 bp. Longer stretches of unique DNA were not observed. The genome contained an unusually high percent-age of inverted repeats: at standard fragment length the zero-time binding fraction amounted to 25% of the genome. Foldback structures ranging from 200 bp to more than 10 kb were observed after S₁-nuclease treatment. They were randomly distributed throughout at least 85% of the genome, and the spacings between them were estimated to be about 1,600 bp on the average. The middle-repetitive DNA (45% of the genome) contained two kinetic components, repeated 430 and 65,000 times per genome, respectively. It was found that the majority of the repetitive sequences are about 300 bp long. Longer repeats (about 2,000 bp) were also observed, comprising a small portion of the genome. The inverted repeats, the middle-repetitive, and the singly-copy sequences were fully interspersed in the genome, thus indicating that R. thomasiana DNA is not organized in either the Xenopus or the Drosophila pattern type. — R. thomasiana is the only mollusc so far in which a satellite DNA has been found. It is organized in tandem repeats of 1,460 bp with a very complex organization but a low degree of divergence.     

Production and utilization of acetate in mammals

1. In an attempt to define the importance of acetate as a metabolic precursor, the activities of acetyl-CoA synthetase (EC 6.2.1.1) and acetyl-CoA hydrolase (Ec 3.1.2.1) were assayed in tissues from rats and sheep. In addition, the concentrations of acetate in blood and liver were measured, as well as the rates of acetate production by tissue slices and mitochondrial fractions of these tissues. 2. Acetyl-CoA synthetase occurs at high activities in heart and kidney cortex of both species as well as in rat liver and the sheep masseter muscle. The enzyme is mostly in the cytosol fraction of liver, whereas it is associated with the mitochondrial fraction in heart tissue. Both mitochondrial and cytosol activities have a K(m) for acetate of 0.3mm. Acetyl-CoA synthetase activity in liver was not altered by changes in diet, age or alloxan-diabetes. 3. Acetyl-CoA hydrolase is widely distributed in rat and sheep tissues, the highest activity being found in liver. Essentially all of the activity in liver and heart is localized in the mitochondrial fraction. Hepatic acetyl-CoA hydrolase activity is increased by starvation in rats and sheep and during the suckling period in young rats. 4. The concentrations of acetate in blood are decreased by starvation and increased by alloxan-diabetes in both species. The uptake of acetate by the sheep hind limb is proportional to the arterial concentration of acetate, except in alloxan-treated animals, where uptake is impaired. 5. Acetate is produced by liver and heart slices and also by heart mitochondrial fractions that are incubated with either pyruvate or palmitoyl-(-)-carnitine. Liver mitochondrial fractions do not form acetate from either substrate but instead convert acetate into acetoacetate. 6. We propose that acetate in the blood of rats or starved sheep is derived from the hydrolysis of acetyl-CoA. Release of acetate from tissues would occur under conditions when the function of the tricarboxylic acid cycle is restricted, so that the circulating acetate serves to redistribute oxidizable substrate throughout the body. This function is analogous to that served by ketone bodies.     

CONSTRICTING ESOPHAGEAL LESIONS—Colon Interposition for Replacement,Combined With Radiotherapy for Carcinoma

The use of colon for esophageal replacement is a procedure that should be considered in the treatment of benign and malignant esophageal lesions. The five-year survival data following operations for carcinoma of the esophagus are not outstanding. The combination of colon transplantation and radiotherapy before and after operation is a procedure that should be utilized if an effort is to be made to increase the survival rate.