Use of latex balls labelled by lectins in the demonstration of Salmonella-Schistosoma mansoni receptor sites

Surface tegumental membrane of adult stage Schistosoma mansoni were examined using the latex sphere coated with Concanavalin A (Con A). Wheat germ agglutinin (WGA) and Protein A (PA). Competitive saccharide inhibitors glucose, mannose and methyl alpha-D-glucopyranoside were used for Con A.     

β-Adrenergic receptor-coupled adenylate cyclase

Beta-adrenergic receptor-coupled adenylate cyclase is regulated by both amplification and desensitization processes. Desensitization of adenylate cyclase is divided into two major categories. Homologous desensitization is initiated by phosphorylation of the receptors by a beta-adrenergic receptor kinase. This reaction serves to functionally uncouple the receptors and trigger their sequestration away from the cell surface. These sequestered receptors can rapidly recycle to the cell surface or, with time, become down regulated, being destroyed within the cell. Dephosphorylation of the receptors is accomplished in the sequestered compartment of the cell, which may functionally regenerate the receptors and allow their return to the cell surface. In heterologous desensitization, receptor function is also regulated by phosphorylation, but in the absence of receptor sequestration or down regulation. In this case, phosphorylation serves only to functionally uncouple the receptors, that is, to impair their interactions with the guanine nucleotide regulatory protein Ns. Several protein kinases are capable of promoting this phosphorylation, including the cAMP-dependent kinase and protein kinase C. In addition to the receptor phosphorylation, heterologous desensitization is associated with modifications at the level of the nucleotide regulatory protein Ns and perhaps Ni. Adenylate cyclase systems are also subject to amplification that involves a protein kinase C-mediated phosphorylation of the catalytic unit of the enzyme. Phosphorylation of the catalytic unit enhances its catalytic activity and results in amplified stimulation by the regulatory protein Ns. Other receptor/effector systems exhibit qualitatively similar regulatory phenomena, suggesting that covalent modification (phosphorylation) may represent a general mechanism for regulating receptor function.     

Inhibitors of Trichoderma reesei β-glucosidase activity derived from autohydrolysis-exploded Eucalyptus regnans

Summary Enzymic saccharification of Eucalyptus regnans pulps pretreated by autohydrolysis-steam explosion resulted in low cellulose conversions into glucose when using trichodermal cellulase preparations. The reduced levels of glucose were attributable to the production of compounds during enzymic hydrolysis which were inhibitory to -d-glucosidase of Trichoderma reesei C-30 and in Meicelase, but not to the cellulases. Aspergillus niger -glucosidase was not inhibited, nor were -d-xylosidase(s) and 1,4--d-xylanase(s). The inhibitory compound(s) could be extracted from the enzymic hydrolyzates with ethyl acetate. The ethyl acetate extractives inhibited -glucosidase in a competitive manner, and inhibitory action was not affected by pH. Addition of the inhibitory compound(s) to trichodermal cellulase digests of cellulose resulted in reduced glucose yields compared to a control. The inhibitory effects could be overcome when cellulase digests were supplemented with A. niger -glucosidase resulting in higher cellulose-to-glucose conversions. The inhibitory compound(s) were localized mainly in the heartwood of E. regnans. An inhibitor compound of this type has not hitherto been reported. The presence of inhibitory compound(s) in the autohydrolysis liquor fraction is also reported.     

The relationship between RNA catalytic processes

Proposals that an RNA-based genetic system preceeded DNA, stem from the ability of RNA to store genetic information and to promote simple catalysis. However, to be a valid basis for the RNA world, RNA catalysis must demonstrate or be related to intrinsic chemical properties which could have existed in primordial times. We analyze this question by first classifying RNA catalysis and related processes according to their mechanism. We define: (A) thedisjunct nucleophile class which leads to 5-phosphates. These include Group I and II intron splicing, nuclear mRNA splicing and RNase P reactions. Although Group I introns and its excision mechanism is likely to have existed in primordial times, present-day examples have arisen independently in different phyla much more recently. Comparative methodology indicates that RNase P catalysis originated before the divergence of the major kingdoms. In addition, alldisjunct nucleophile reactions can be interrelated by a proposed mechanism involving a distant 2-OH nucleophile. (B) theconjunct nucleophile class leading to 3-phosphates. This class is composed of self-cleaving RNAs found in plant viruses and the newt. We propose that tRNA splicing is related to this mechanism rather than the previous one. The presence of introns in tRNA genes of eukaryotes and archaebacteria supports the idea that tRNA splicing predates the divergence of these cell types.     

Characterization of the calcium sensitivity of differentiation in SCC-13 human squamous carcinoma cells

Summary The sensitivity to calcium of the human squamous carcinoma cell line, SCC-13, was demonstrated and characterized. Cultures grown to confluence in the presence of 0.2 to 2 mM calcium had approximately 10-fold higher levels of particulate transglutaminase activity and envelope competence than those grown in low calcium (0.025 to 0.05 mM) medium. Raising the calcium from 0.025 to 1.8 mM induced expression of this enzyme and of competence over the course of a week. Conversely, for cultures grown to confluence in 1.8 mM calcium, subsequent reduction of calcium to 0.025 mM resulted in a substantial decline in transglutaminase over a similar time period. Immunoprecipitable transglutaminase was clearly identifiable in cultures grown in 1.8 mM calcium-containing medium but not in those grown in low calcium medium or in the presence of retinoic acid, suggestive of regulation at the level of mRNA accumulation or translation rather than posttranslational modification. This research was supported by Public Health Service grant AR 27130 from the National Institute of Arthritis, Musculoskeletal and Skin Diseases, Bethesda, MD, and National Research Service postdoctoral fellowship ES 05336 from the National Institute of Environmental Health Sciences, Research Triangle Park, NC.     

Demographic responses of arctic hares Lepus arcticus placed on two predominantly forested islands in Newfoundland

During January-April 1989. we monitored survival, reproduction, and body condition of 19 radio-collared arctic hares Lepus areticus introduced to two predominantly (80%) forested islands. Merchant (66 1 ha) and Burke (82 6 ha), in Placentia Bay, Newfoundland By late April, bone-marrow fat (42 7%) and kidney fat indices were lower than found in populations on the mountain barrens of western Newfoundland However, most island hares gained weight overwinter, and litter sizes (mean. 4 2 in utero) and testis weights (mean, 8 3 g) were as large or larger than recorded from other introduced and natural populations in Newfoundland The distribution of telemetry locations, tracks and feeding sites indicated that hares frequented the scattered barrens (totalling c 30 ha) on both islands in greater proportion than available These results suggest that, in the absence of snowshoe hares and mammalian predators, forested regions interspersed with small patches of barrens can sustain arctic hares     

Identification and sequence of a Na+-linked gene from the marine bacterium Alteromonas haloplanktis which functionally complements the dagA gene of Escherichia coli

A 4.0 kb fragment from a plasmid genomic DNA library of the marine bacterium Alteromonas haloplanktis ATCC 19855 was found in the presence of Na+ to complement the dagA gene of Escherichia coli. We have completely sequenced this fragment and the position of the Na(+)-linked D-alanine glycine permease gene (dagA) on the fragment has been determined by complementation. The predicted carrier protein consists of 542 amino acid residues (M(r) 58,955). Its hydropathy profile suggests it is composed of eight transmembrane segments with a long hydrophilic region between segments six and seven. Significant similarity has been found between this Na(+)-linked permease and the Na+/proline permeases of E. coli and Salmonella typhimurium and the human and rabbit intestinal Na+/glucose cotransporters.