Lectin-induced modulation of the antibody response to type III pneumococcal polysaccharide

Several lectins were tested for their capacity to alter the antibody response to type III pneumococcal polysaccharide (SSS-III). The antibody response was enhanced by concanavalin A (Con A), phytohemagglutinin (PHA), as well as lectins from Phytolacca americana (Pa-2), Pisum sativum (PSA), and Lens culinaris (LCH), when these lectins were given 2 days after immunization with SSS-III; however, suppression was obtained when Con A and Pa-2 were given at the time of immunization. By contrast the lectins from Vicia villosa (VVL) and Bauhinia purpurea (BPA) did not alter the antibody response. Since the lectins PSA and LCH bind to the same monosaccharide as Con A, whereas the other lectins bind to different monosaccharides, these findings indicate that there is no relationship between nominal monosaccharide specificity and the capacity to modulate the antibody response. Substantial increases in the magnitude of the IgG₁ antibody response was noted after the administration of Con A whereas profound enhancement of IgG_2a antibody response was noted after PHA was given.     

A general method for visualizing enzymes releasing adenosine or adenosine-5′-monophosphate

Biochemical Genetics -     

The effects of various nutritional supplements on the growth,migration and differentiation ofxenopus laevis neural crest cells in vitro

Summary This study investigates the nutritional requirements ofXenopus laevis neural crest cells and melanophores developing in vitro. A comparison is made between the growth and differentiation of cells in serum-containing medium and a chemically defined, serum-free medium that we have designed. Our chemically defined medium is more efficient than serum-supplemented medium in promoting proliferation of these cells. Several supplements are required to enhance culture development. These include insulin, α-melanocyte stimulating hormone, somatotropin, luteotrophic hormone, linoleic acid, uridine, and putrescine. In addition, collagen and fibronectin provide the most conductive environment tested for cell migration and adhesion. This work was supported by establishment and major equipment grants from the Alberta Heritage Foundation for Medical Research to N. C. M. Nadine C. Milos is a Heritage Medical Research Scholar of the Alberta Heritage Foundation for Medical Research.     

The disappearance of isocitrate lyase from the green alga Chlorella fusca studied by immunoprecipitation

When acetate-adapted cultures of Chlorella fusca were transferred to nitrogen-free medium containing glucose, isocitrate lyase activity was lost over a period of about 25 h. Using a combination of in vivo isotope labelling and immunoprecipitation with anti-isocitrate lyase IgG it was shown that: 1. The onset of loss of enzyme activity preceeded the complete cessation of enzyme synthesis. 2. Disappearance of isocitrate lyase activity was accompanied by loss of enzyme protein, without accumulation of antigenic protein distinguishable from the normal subunit polypeptide of the enzyme, as judged by SDS gel electrophoresis of immunoprecipitated samples from supernatant cell-free extracts. 3. SDS gel electrophoresis of immunoprecipitated isocitrate lyase revealed the presence of antigenic protein bands of M_r about twice that of the normal subunit polypeptide, but the appearance of these apparent dimer forms did not obviously correlate with enzyme degradation. 4. Isoelectric focusing of immunoprecipitated isocitrate lyase showed that the enzyme became progressively more oxidised during the period of its degradation in vivo. 5. By titrating crude broken cell suspensions with anti-isocitrate lyase antibody, preliminary evidence was obtained for transfer of the enzyme from the soluble fraction to an insoluble form as part of the process of disappearance.     

Acceptors for cyclic AMP-dependent and calcium ion-dependent protein kinases in rat brain cytosol fractions: A comparison of occluded (synaptosomal) cytosol with non-occluded cytosol

Endogenous protein phosphorylation patterns were compared in occluded and non-occluded cytosol fractions prepared from rat forebrain. The occluded fraction was taken as representative of synaptosomal cytosol. One- and two-dimensional autoradiographs revealed the presence in non-occluded cytosol of a substrate for cAMP- and Ca²⁺/calmodulin-dependent protein kinase activities of M_r 300kD, corresponding to phosphorylated microtubule-associated protein-2 (MAP-2); this protein was absent in occluded cytosol. In contrast, a major substrate for protein kinase C was observed exclusively in occluded cytosol after phosphorylation under basal conditions. However, after phosphorylation in the presence of exogenous lipids, approximately equal amounts of the 82kD substrate were detected in both fractions, suggesting that protein kinase C in the occluded fraction was present in a partially activated state. Other minor differences in phosphorylation patterns between the two fractions were observed.Special Issue dedicated to Prof. Eduardo De Robertis.     

Kinetic studies on the chymotrypsin Aα-catalyzed hydrolysis of a series of N-acetyl-l-phenylalanyl peptides

A series of N-acetyl-l-phenylalanyl peptides of general formula Ac-Phe-(Gly)_n-NH₂ (n = 0–2) has been synthesized to study the effect of leaving group chain length on the efficiency of chymotrypsin A_α amidase and peptidase activities. The effect upon catalysis of hydrophobic side chains on the leaving group was investigated using similar substrates with one of the glycine residues selectively substituted by an alanine residue as in AcPheAlaNH₂, AcPheAlaGlyNH₂, and AcPheGlyAlaNH₂. Values of k_cat and K_m have been obtained from kinetic measurements at pH 8.00 and 25 °C. The results are shown to be consistent with binding schemes postulated from published model building studies. The catalytic reactions were studied over a range of temperature (15–35 °C) and in each case the Arrhenius law was obeyed. It was thus possible to obtain meaningful values for the thermodynamic functions of activation for the acylation step of the catalytic reaction. The results are shown to confirm the findings of postulated binding schemes but indicate that conclusions drawn from kinetic measurements at a single temperature may sometimes be misleading.     

Population Dynamics of Meloidogyne incognita and Rotylenchulus reniformis Alone and in Combination,and Their Effects on Sweet Potato

Meloidogyne incognita (Mi) and Rotylenchulus reniformis (Rr) interactions on sweet potato were studied in naturally and artificially infested field plots for 3 years. In a naturally infested field, early season counts of Mi or Rr were positively correlated with later counts of the same nematode, but negative correlations were found between early Mi and subsequent Rr, and early Rr and subsequent Mi counts. In field plots fumigated with methyl bromide and then infested with low levels of Rr, Mi, and Rr + Mi, final population densities of Mi juveniles were reduced by Rr, but Rr was not affected by Mi. In field plots with a high natural population density of Rr, artificial infestation with high levels of Mi in both fumigated and nonfumigated treatments inhibited Rr, while the final Mi juvenile population density was not affected. Results indicate that a competitive interaction exists with each species capable of inhibiting the other and becoming the dominant population. The nematodes had no apparent effect on yield at the inoculum densities used, either alone or mixed. Both nematodes increased cracking of sweet potatoes, but mixed populations did not differ in incidence of cracking from either Rr or Mi alone.