R-prime plasmids from Bradyrhizobium japonicum and Rhizobium fredii

The formation of R-prime plasmids was selected in crosses involving soybean microsymbionts with genomic Tn5 insertions and carrying plasmid pJB3JI (with one IS2) copy as donors and Escherichia coli HB101 as recipient. Whereas the parent plasmid was 60 kb, recombinant plasmids between 76 kb and 121 kb were obtained. Restriction and Southern analyses confirmed the mobilization of Tn5 on four R-primes from Bradyrhizobium japonicum I-110 and on an R-prime plasmid from Rhizobium fredii HH303. The largest R-prime plasmid was obtained from the rescue of two symbiotically defective R. fredii mutant strains that required adenosine.Non-standard abbreviation TDP transposon donor pool Scientific article number A-4728 and contribution number 7724 of the Maryland Agricultural Experiment Station     

Conflicting evidence regarding the transport of alpha-glutamyl-dipeptides by human erythrocytes.

A novel ninhydrin-positive compound, N-methyl-D-aspartic acid, was identified in the muscle extracts of the blood shell, Scapharca broughtonii. This compound is already known to have potent neuroexcitatory activity, inducing hypermotility and strong releasing action of serum luteinizing hormone in mammals. This may be, however, the first finding of N-methyl-D-aspartic acid in natural products.     

Stereospecificity and requirements for activity of the respiratory NADH dehydrogenase of Escherichia coli

The respiratory NADH dehydrogenase of Escherichia coli has been further amplified in vivo by genetic methods. The enzyme, a single polypeptide of Mr 47 200 of known amino acid sequence [Young, I. G., Rogers, B. L., Campbell, H. D., Jaworowski, A., & Shaw, D. C. (1981) Eur. J. Biochem. 116, 165-170], constitutes 10-15% of the total protein in the amplified membranes. In situ in the membrane, the enzyme contains 1 mol of FAD/mol of subunit and has a specific NADH:ubiquinone-1 oxidoreductase activity of approximately 1100-1200 units mg-1 at 30 degrees C, pH 7.5. The purified enzyme contains phospholipid, which remains closely associated with it during gel filtration on Sephacryl S-300 in the presence of 0.1% (w/v) cholate at low ionic strength. Under these conditions the enzyme is extensively aggregated (apparent Mr greater than 10(6]. This procedure yielded enzyme with a specific activity of 980 units mg-1, similar to the value observed in the membrane. This preparation contained less than 0.1 mol of Fe/mol of enzyme, confirming that Fe is not involved in reduction of ubiquinone 1 catalyzed by the enzyme. Neutron activation analysis of purified enzyme has demonstrated the absence of 35 trace elements including Se, Zn, Mn, Co, W, Cu, and Fe. The enzyme polypeptide, prepared completely free of phospholipid, FAD, and ubiquinone by gel filtration in the presence of sodium dodecyl sulfate, has been reactivated. The results show that the only components necessary for catalysis of ubiquinone-1 reduction by NADH in this system are the enzyme polypeptide, FAD, and phospholipid.(ABSTRACT TRUNCATED AT 250 WORDS)