Genes encoding alpha-heavy chains of rabbit IgA: characterization of cDNA encoding IgA-g subclass alpha-chains

cDNA molecules encoding rabbit IgA alpha-heavy chains have been synthesized and six of these have been characterized. The complete nucleotide sequence of one cDNA, p 19 (942bp), showed that it encoded all but the N-terminal 57 amino acid residues of the constant region of alpha-chains. The cDNA molecules were subcloned into the expression vector pUC8 and E. coli were transformed. Radioimmunoassay of the molecules synthesized by these clones showed that all six cDNA molecules encoded alpha-chains of the IgA-g subclass. Comparison of the amino acids encoded by the alpha-cDNA with the amino acid sequence of mouse and human alpha-chains showed that although all of the intradomain disulfide bonds appear to be conserved, some positions, probably involved in interchain disulfide bonds, are not conserved. We propose that secretory component is covalently bound to cysteine 299 and/or cysteine 301 of the CH2 domain of mouse and human alpha-chains. The results from Southern blot analysis of genomic DNA with 32P-cDNA suggests that the rabbit genome has multiple C alpha genes.     

Effect of insulin and prednisolone on cyclic nucleotides and phosphoenolpyruvate carboxykinase activity in brown fat and liver of developing rats

The concentrations of cyclic AMP and cyclic GMP in brown fat and liver of both suckling and adult rats at fixed times after injection of insulin (2.5 U/100 g body weight) or prednisolone (2.5 mg/100 g body weight) were compared with the activity of phosphoenolpyruvate carboxykinase assayed 24 h after the injections. A stimulus that produced an increase in cyclic AMP content also produced an increase in the enzyme activity. If the content of cyclic GMP was also increased there was no rise in phosphoenolpyruvate carboxykinase activity. A rise in the content of cyclic GMP alone was associated with a reduction in the activity of the enzyme. These preliminary results indicate that cyclic AMP could be involved in the induction of phosphoenolpyruvate carboxykinase and that cyclic GMP may somehow be related to its repression. The known differences in the response of phosphoenolpyruvate carboxykinase activity to insulin and prednisolone in different tissues and at different stages of ontogenic development may thus be linked to differences in the responsiveness of enzymes concerned with the metabolism of cyclic nucleotides.     

Biology of Azospirillum-Sugarcane Association: Enhancement of Nitrogenase Activity

Azospirillum brasilense was reisolated from associations with callus tissue cultures of sugarcane and compared with stock cultures of the inoculated bacterium and related strains. Although the reisolate had a growth rate similar to stock cultures, it exhibited a severalfold increase in maximum specific activity of nitrogenase. The reisolate and the parent culture had similar ultrastructure. The general ultrastructure of Azospirillum is described. The bacterium was capsulated when grown on nitrogen-free nutrient agar plates and on callus, but was not capsulated when growing in a subsurface zone in N-free semisolid nutrient agar, except rarely in aging cultures. Capsulation may be a protective mechanism against unfavorable pO₂ under dinitrogen-fixing conditions. Pleomorphism occurred in capsulated forms, and the ultrastructure of these forms is described.