Coprecipitating IgG asymmetric antibodies: A possible role for Fab glycosylation,and speculations on their formation and functions in disease

IgG asymmetric antibodies are synthesized by the same cellular clones as the symmetric ones but appear in the immune response in different proportions. The evidence suggests that they are caused by asymmetric glycosylation on some IgG molecules in the Fab region. The cause of this is unknown but it could be speculated that there are cellular factors that induce glycosyl transferases or cause the molecule to be more accessible to glycosylation. The production of asymmetric antibodies can be modified by the physical status (soluble or particulate) of the antigen used as immunogen by the number and frequency of stimulation, and by physiological factors such as the ones secreted by the placenta and by lymphocytes that express progesterone receptors in response to hormone. An increase of these antibodies can be beneficial or harmful to the host, depending on the situation in which they act and the character of self or non-self of the antigens recognized. Editors note—Many of the ideas proposed in this article are very speculative, but it was thought appropriate to publish it in order to stimulate further discussion of the subject. It is an interesting role for Fab glycosylation that is proposed by Professor Margni. The ideas discussed are not necessarily those held by the Editorial Board or the reviewers, who felt that the evidence for many of the deductions made was very limited. It was also emphasized by the reviewers that the author's case would be substantially improved if more corroborative evidence was available from other groups. The Editors would welcome any comments on the subject for publication in future issues of the journal.     

Occurrence of subcutaneous zygomycosis (Entomophthoromycosis Basidiobolae) caused by Basidiobolus haptosporus with pulmonary involvement

A case of a two-year-old boy with multiple subcutaneous lesions caused by Basidiobolus haptosporus is presented.The child had also a non-toxic familial goiter and clinical and radiological features of a pulmonary illness. The pulmonary manifestations only disappeared with the treatment with potassium iodide. The authors think that the pulmonary lesions must have arisen by direct spread of the fungus from the subcutaneous lesions of the chest.     

Formaldehyde-induced appearance of septate junctions between digestive vacuoles

Tissue biopsies from (1) some chronic inflammatory diseases, (2) a necrotic tumoral process, (3) normal human lymphatic ganglia, and (4) two congenital diseases of the adrenal cortex were selected for study. A block from each biopsy was fixed in glutaraldehyde-paraformaldehyde; a second block was fixed in 10% formaldehyde. In all cases septate junctions between digestive vacuoles did occur in phagocytic cells and some adrenal cortex cells fixed in formaldehyde. These junctions were similar to those reported recently for malakoplakia phagocytes. Consistently, they were not found to attach organelles other than lysosomes derivatives. Both phagocytes and adrenal cortex cells in the material fixed in glutaraldehyde-paraformaldehyde did not display adhesive specializations between digestive vacuoles. This suggests that the septate junctions described herein are artifactuous structures induced by formaldehyde. There is, however, a certain degree of specificity of cells having the capability of developing these septate junctions. It is assumed that the coating material of digestive organelles in phogocytes and some other cells would be responsible for both cell specificity and organelle specificity of the formaldehyde-induced septate junctions.     

Effect of streptozotocin diabetes on some urea cycle enzymes

Streptozotocin induced diabetes in rats increased the activities of the three mitochondrial enzymes, carbamylphosphate synthetase, ornithine transcarbamylase and N-acetylglutamate synthetase, but not of the cytosolic N-acetylglutamate deacylase. Levels of both N-acetylglutamate and arginine, which are activators of carbamylphosphate synthetase and N-acetylglutamate synthetase respectively, increased in diabetes. These results serve to explain the increase both of mitochondrial citrulline and urea formation in hepatocytes and the increased urea excretion in diabetes.     

Stringent response and initiation of secondary metabolism in Streptomyces clavuligerus

Cephalosporin biosynthetic activity and extracellular protease production increased during growth of Streptomyces clavuligerus in defined medium, while the level of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) remained very low and stable. Cephalosporin biosynthesis (measured in resting cell systems) was initiated during early exponential growth in complex media, without appreciable change in the small ppGpp pool. Nutritional shift-down induced by withdrawal of Casamino acids caused a transient increase in ppGpp and a reduction of RNA accumulation. The increase in ppGpp was small in very young cultures, but increased as the culture aged. Twenty-seven spontaneous thiostrepton-resistant mutants were isolated and partially characterized. Most of them had a reduced ppGpp-forming ability and gave normal titres of cephalosporin. However, in complex medium, some mutants did not produce cephalosporins or extracellular protease, whereas others overproduced cephalosporins. The results indicate that, in S. clavuligerus, there is no obligatory relationship between the initiation of secondary metabolism and the stringent response.     

Cloning, sequencing, and mutational analysis of the Bradyrhizobium japonicum fumC-like gene: evidence for the existence of two different fumarases.

The Bradyrhizobium japonicum fumarase gene (fumC-like) was cloned and sequenced, and a fumC deletion mutant was constructed. This mutant had a Nod+ Fix+ phenotype in symbiosis with the host plant, soybean, and growth in minimal medium with fumarate as sole carbon source was also not affected. The cloned B. japonicum fumC gene fully complemented an Escherichia coli Fum- mutant, strain JH400, for growth in minimal medium with fumarate. The predicted amino acid sequence of the FumC protein showed strong similarity to the E. coli FumC protein, Bacillus subtilis CitG protein, Saccharomyces cerevisiae Fum1 protein, and the mammalian fumarases. The B. japonicum FumC protein accounted for about 40% of the total fumarase activity in aerobically grown cells. The remaining 60% was ascribed to a temperature-labile fumarase. These data suggest that B. japonicum possesses two different fumarase isoenzymes, one of which is encoded by fumC. Besides E. coli, which has three fumarases, B. japonicum is thus the second bacterium for which there is genetic evidence for the existence of more than one fumarase.     

Changes in force and calcium sensitivity in the developing avian heart.

The aim of this study was to characterize the development of the contractile properties of intact and chemically skinned muscle from chicken heart and to compare these characteristics with those of developing mammalian heart reported by others. Small trabeculae were dissected from left ventricles of Arbor Acre chickens between embryonic day 7 and young adulthood (7 weeks post-hatching). At all ages, increasing extracellular calcium (0.45-3.6 mM) progressively increased twitch force of electrically stimulated trabeculae. Twitch force at 1.8 mM extracellular calcium, normalized to cross-sectional area, increased to a maximum at 1 day post-hatching, remained constant through 3 weeks post-hatching, but then decreased at 7 weeks post-hatching. The maximal calcium-activated force of trabeculae chemically skinned with Triton X-100 detergent increased to a maximum 2 days before the time of hatching and was not significantly changed up to 7 weeks post-hatching. Over the ages studied, average twitch force in 1.8 mM calcium was between 26 and 66% of maximal calcium-activated force after skinning, suggesting that the contractile apparatus is not fully activated during the twitch in normal Ringer. In skinned trabeculae, the calcium sensitivity of the contractile apparatus was higher in the embryo than in the young adult. These age-dependent changes in calcium sensitivity are correlated with isoform switching in troponin T. A decrease in pH from 7.0 to 6.5 decreased the calcium sensitivity of the contractile apparatus to a greater degree in skinned trabeculae from young adult hearts than in those from embryonic hearts. This change in susceptibility to acidosis is temporally associated with isoform switching in troponin I.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetics of a model of autocatalysis, coupling of a reaction in which the enzyme acts on one of its substrates.

A global kinetic analysis is presented of a model of an enzyme autocatalytic process, to which a reaction is coupled, in which the enzyme acts upon one of its substrates. The kinetic equations of both the transient phase and the steady state are derived for this mechanism. In addition, we determine the corresponding kinetic equations for several particular cases which are characterized by certain relations between the rate constants. Finally, a kinetic data analysis is proposed for one of these particular cases. It can easily be extended to any of the other cases.