The process of ozone depletion over the Antarctic continent has resulted in the increase of incident ultraviolet-B (UVB) radiation, whose effects may be damaging to living organisms. To counteract the negative effects of ultraviolet radiation (UVR), aquatic organisms may display one or more strategies: (1) avoidance (i.e. deep distribution); (2) photoprotection through the use of ''sunscreen'' compounds, such as mycosporine-like amino acids (MAAs); and (3) enzymatic repair of the damage. The effects of UVR were assessed on four populations of the copepod Boeckella poppei from Antarctic lakes using laboratory and field experiments. The results were related to measurements of DNA enzymatic repair activity and MAA concentration. This is the first study that combines these measurements in zooplankton. Boeckella poppei was highly tolerant to UVR (LD 50 ϭ 2.2-2.78 J cm Ϫ2 ). However, measurements of photorecovery (comparison of UVB mortality in the presence and absence of photoreactivating light) and dosage of photolyase activity indicated low rates of enzymatic repair, which may be the result of low temperatures typical of Antarctic lakes. Three different MAAs were identified, both in phytoplankton and copepods: porphyra-334, mycosporine-glycine, and shinorine. The population of B. poppei from Lake Boeckella had the lowest MAA concentration, as well as the lowest tolerance to artificial and natural UVR. These findings support the idea that UV tolerance in this species is related to the accumulation of MAAs. A comparison of the strategies used to cope with potentially damaging levels of UVR by different species of Boeckella indicates a high degree of plasticity in this genus, which has probably been key for its success to colonize a wide range of UV environments.

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cysB and cysE strains were obtained as spontaneous mecillinam-resistant mutants of Salmonella typhimurium. The resistance to mecillinam was caused by the cys mutations which also conferred tolerance to lethal cell shape mutations. Most, but not all, cysB and cysE mutations from other origins displayed the same behavior. Resistance was abolished by O-and N-acetylserine in cysE mutants; by thiosulfate, sulfite, and sulfide in cysB mutants; and by cysteine in both types of mutants. It is concluded that an event involved in mecillinam action requires the inducer and the activator protein of the cysteine regulon.

In the present work, interactions between three Lactobacillus strains (Lactobacillus fermentum CRL1015, Lactobacillus animalis CRL1014, and Lactobacillus fermentum CRL1016) and chicken small intestinal mucus were determined. Three lactobacilli isolated from chicken and selected by their potentially probiotic properties were able to grow in mucus preparations. Three peaks from gel filtration chromatography of intestinal mucus were obtained. The adhesion to three mucus fractions (I, II, and III), especially fraction III, was higher (P < 0.01) in L. fermentum CRL1015 than L. animalis CRL1014. Pretreatment of this fraction with proteases and metaperiodate showed lower (P < 0.01) adhesion values than that of the control, suggesting that a glycoprotein from the mucus acts as a receptor for L. fermentum CRL1015. Highest adhesion values were obtained at pH 7 and 42 degrees C, and neither the removal of divalent cations with ethylenediaminetetraacetic acid (EDTA) nor the addition of calcium produced significant variation from the adhesion values of the control (P > 0.01). This adhesion was only inhibited by N-acetyl-glucosamine. Salmonella pullorum and Salmonella gallinarum showed high (P < 0.01) values of adhesion to chick intestinal mucus. The results obtained from assays of the inhibition of adherence of Salmonella spp. to mucus, immobilized in polystyrene tissue culture wells, indicated that the pathogen adhesion was not reduced by lactobacilli (P > 0.05) or their spent culture supernatants (P > 0.05), suggesting that these strains did not interfere with the binding sites for Salmonella spp. adhesion to the small intestinal mucus.

Three monomeric procarboxypeptidases and a binary complex consisting of a procarboxypeptidase and a chymotrypsinogen have been isolated from rat pancreas by HPLC. N-terminal sequence determination, substrate-specificity analysis and physico-chemical characterization showed that the carboxypeptidase precursors were the Al, A2 and B forms. No isomorphism could be detected for any of these proenzymes and no clear evidence was obtained for the presence of procarboxypeptidase-containing quaternary complexes of the types previously described for other species. Instead, we observed the presence of a binary complex between procarboxypeptidase A2 and chymotrypsinogen B. Among the major pancreatic endoproteinases, only trypsin was found to be a general activator of rat procarboxypeptidases in vitro. Time-course analysis of the products generated after trypsin addition confirmed that full activation of procarboxypeptidase A1 requires several cleavages in the C-terminal region (residues 87 -94) of the activation segment, while procarboxypeptidases A2 and B require a single cleavage each. The carboxypeptidases released participate in the trimming of the activation segment in A1 and B, but not in A2, probably because of the high specificity of the latter in the active form.The present knowledge about the precursor forms of pancreatic metallo-pro-carboxypeptidases (Metallo-pro-CP) has been obtained from studies on many different species [l]. A significant point in this progress was the gene cloning and sequence analysis of pro-CP Al, A2 and B from rat pancreas [2, 31. Together with these studies, the functional mapping of the active site of the rat carboxypeptidase A1 isoform (CPA1) by site-directed mutagenesis [4, 51, and the X-ray crystallographic analysis of rat carboxypeptidase A2 (CPA2) [6], made the rat system suitable to serve as one of the reference models in the field. However, the properties of the pro-CP complement in rat pancreas have not been evaluated. These characteristics are now determined.Pro-CP occur in a diversity of isoforms and alleloforms in the pancreas of vertebrates [7-91. Two isoforms of pro-CPB and pro-CPA (Bl, B2, A1 and A2) are found in certain species, and pro-CPA is found in at least two alleloforms in bovine pancreas. We now show that three of the isoforms mentioned, Al, A2 and B, are found and expressed at similar levels in rat pancreas. In addition to the monomeric forms [9-111, pro-CPA also occur in different oligomeric complexes with other pancreatic zymogens [9,11-151. A question remains open about the potential role of these complexes and the reason for the species dependence of their occurrence, as ternary complexes in ruminants and as binary complexes in non-ruminants [13]. In rat pancreas we find that a fraction of pro-CPA2 is complexed with a chymotrypsinogen-like zymogen of the B form. Such a binary complex has no counterpart in other species, where only binary complexes between pro-CPAl and either propancreatopeptidase E [9, 11, 161 or chymotrypsinogen C [17] have been described.R...