Resialylation of sialidase-treated sheep and human erythrocytes by Trypanosoma cruzi trans-sialidase: restoration of complement resistance of desialylated sheep erythrocytes.

Trypanosoma cruzi trans-sialidase (TS) is a recently described enzyme which transfers alpha(2-3)-linked sialic acid from host-derived sialylated glycoconjugates to parasite surface molecules [Schenkman et al. (1991) Cell, 65, 1117]. We report here on the ability of TS to transfer sialic acid from donor sialyl-alpha(2-3)lactose to sialidase-treated sheep and human erythrocytes. Up to approximately 50% resialylation of both desialylated red cells could be attained. Resialylation of desialylated sheep erythrocytes restores their resistance to lysis by human complement. This ascribes a possible biological role for T. cruzi TS and demonstrates directly that sialic acid is solely responsible for preventing alternative pathway activation of human complement by sheep erythrocytes.     

Author index to volume 200

Biochemical and partial sequence data reveal the two-domain structure of p36. A loose structure of some 30 residues at the amino-terminus contains the phosphorylatable tyrosine and the binding site for the p11 regulatory chain. The following p33 domain retains the lipid-binding site as well as the Ca2+ site which influences the spectral properties of the single tryptophan and one tyrosine. The combined sequence data covering about 25% of the molecule identify p36 as a unique polypeptide.     

Methodological problems in evolutionary biology VII. The species plague

Various philosophers and evolutionary biologists have recently defended the thesis that species are individuals rather than sets. A decade of debates, however, did not suffice to settle the matter. Conceptual analysis shows that many of the key terms involved (individuation, evolutionary species, spatiotemporal restrictedness, individual) are ambiguous. Current disagreements should dissolve once this is recognized. Explication of the concepts involved leads to new programs for philosophical research. It could also help biology by showing how extant controversies concerning evolution may have conceptual rather than factual roots.     

Dynamics of bryophytes in a chalk grassland

Dynamics of bryophytes were followed in a chalk grassland in 4 plots, 25×25 cm, each subdivided in to 400 subplots, in which every 3–4 months the presence of all bryophyte species was recorded. During the first 14 months no successional trends were visible. However, dynamics on the scale of one subplot were considerable. Degree of dynamics was markedly negatively correlated with original presence in the plots. Several explanations for this correlation are discussed.     

Protein-chemical identification of the major cleavage sites of the Ca2+ proteinase on murine vimentin, the mesenchymal intermediate filament protein

Neutral thiol proteinases (calpains), activated by calcium are involved in the intracellular turnover of intermediate filaments but the precise position of the cleavage points has remained unknown. Here we identify by direct sequence analysis the major cleavage sites found when murine vimentin is digested by limited proteolysis in vitro with calpain purified from porcine kidney. Contrary to some previous suggestions, no absolute sequence specifity could be detected although 10 specific sites have been identified. This result is in line with the cDNA derived amino-acid sequence of a calpain, which pointed to a similarity of the catalytic site with the active sites in papain, cathepsin and actinidin. However, all major cleavage sites are located within regions of the vimentin molecule, which in current models of intermediate filament structure are thought to be non-helical: the amino-terminal headpiece, the carboxy-terminal tailpiece and the spacer separating the two major coiled-coil domains. The sequence information about the cleavage sites was extended to provide the amino-terminal 119 residues of murine vimentin.     

Responses of a Mutant Strain of Chlamydomonas reinhardi to Prolonged Organotrophic Growth

The responses of the wild type strain and of the y-2 mutant strain of Chlamydomonas reinhardi to long term organotrophic growth were studied. It was shown that wild type can be cultured as an organotroph for at least a month with little decrease in chlorophyll content and no loss of viability. On the other hand, the mutant strain y-2 dies during such organotrophic growth, death beginning after 5 to 6 days in the dark. The kinetics of death indicate that the loss of 95% of the chlorophyll precedes death and that revertants to wild type overgrow such a culture. The results suggest that death of y-2 is correlated with the loss of chlorophyll rather than simple metabolic response to organotrophy and that the chloroplast or a chloroplast related factor may perform certain nonphotosynthetic functions in C. reinhardi. The activities of nicotine adenine dinucleotide and nicotine adenine dinucleotide phosphate dependent triose phosphate dehydrogenases were studied during long term organotrophic growth of y-2. It was found that the activities of these enzymes varied in a manner consistent with previous findings under these conditions. The activity of glutamic dehydrogenase was found to vary as a function of chlorophyll content in the mutant strain y-2.     

A single cDNA encodes two isoforms of stathmin, a developmentally regulated neuron-enriched phosphoprotein

Stathmin, a 19-kDa neuron-enriched soluble phosphoprotein, has been recently proposed as an ubiquitous intracellular relay for the diverse extracellular signals regulating cell proliferation, differentiation, and functions through various second messenger pathways (Sobel, A., Boutterin, M.C., Beretta, L., Chneiweiss, H., Doye, V., and peyro-Saint-Paul, H. (1989) J. Biol. Chem. 264, 3765-3772). Internal sequences of the protein from rat brain were determined after purification by two-dimensional polyacrylamide gel electrophoresis, electrotransfer onto Immobilon, and in situ proteolysis. Oligonucleotide mixtures based on these sequences were used to clone a cDNA for stathmin from a rat PC12 cell lambda gt 10 library. The deduced amino acid sequence reveals partial homologies with the coiled coil structural regions of several intracellular matrix phosphoproteins. Using this cDNA as a probe, we show that the expression of stathmin mRNA parallels that of the protein during brain ontogenesis, reaching a maximum at the neonatal stage. In vitro translation of the derived cRNA yielded all the known molecular forms of stathmin, namely its alpha and beta isoforms in their unphosphorylated and phosphorylated states. Thus, a single cDNA codes for both biologically relevant isoforms of the protein, indicating that they differ by co- or post-translational modifications.     

Evaluation of two unstructured mathematical models for the penicillin G fedbatch fermentation

The mathematical model for the penicillin G fed-batch fermentation proposed by Heijnen et al. (1979) is compared with the model of Bajpai & Reuß (1980). Although the general structure of these models is similar, the difference in metabolic assumptions and specific growth and production kinetics results in a completely different behaviour towards product optimization. A detailed analysis of both models reveals some physical and biochemical shortcomings. It is shown that it is impossible to make a reliable estimation of the model parameters, only using experimental data of simple constant glucose feed rate fermentations with low initial substrate amount. However, it is demonstrated that some model parameters might be key factors in concluding whether or not altering the substrate feeding strategy has an important influence on the final amount of product.It is illustrated that feeding strategy optimization studies can be a tool in designing experiments for parameter estimation purposes.