Mutagenic activity of nine N,N-disubstituted hydrazines in the Salmonella/mammalian microsome assay.

The mutagenic activity of N,N-dimethyl-, N,N-diethyl-, N,N-dibutyl-, N,N-diisobutyl-, N,N-di(p-tolyl)-, N-ethyl-N-phenyl-, N,N-dibenzyl-, N,N-diphenyl- and N,N-diisopropylhydrazine was examined in the Salmonella/mammalian microsome assay using the strains TA1535, TA1537, TA97, TA98, TA100, TA102 and TA1530. All nine hydrazines were mutagenic in at least one tester strain, although of borderline significance for some of the compounds. The mutagenic potencies of the hydrazines varied 2-3 orders of magnitude, from very weak to moderate mutagenic activity. In general, the addition of S9 resulted in a lowering of the mutagenic activity and a lowering of the toxic properties of the hydrazines. The test results were relatively difficult to evaluate due to toxic effects of many of the test compounds on the test bacteria which may have resulted in an underestimation of the mutagenic potencies of some of the compounds. The pattern of mutagenic activity of the hydrazines in the different tester strains indicates that more than one mechanism of action may be involved in the mutagenicity.     

Antitumour activities of levans produced by Zymomonas mobilis strains

Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect.     

Biosynthesis of intestinal microvillar proteins. Low temperature arrests both processing and intracellular transport

The effect of culture at 20 degrees C on biosynthesis of microvillar enzymes was studied in pig small intestinal mucosal explants. At this temperature, aminopeptidase N (EC 3.4.11.2) and sucrase-isomaltase (EC 3.2.1.48-10) both accumulated intracellularly, predominantly in their transient, high mannose-glycosylated form characteristic of the newly synthesized enzymes prior to the molecular processing taking place in the Golgi complex. The general morphology of the enterocyte was unaffected by culture at low temperature except for the Golgi complex where the cisternae appeared condensed and surrounded by numerous vesicles of 50 to 55 nm. Both molecular processing and microvillar expression could be restored by shifting the temperature to 37 degrees C. Culture at low temperature did not induce any missorting of newly synthesized aminopeptidase N, but both molecular processing and microvillar expression only resumed at a slow rate after increasing the temperature, suggesting that reorganization of the Golgi complex is a time-requiring process.     

Rotational correlation times of peptides determined by perturbed angular correlations of γ-rays

The technique of Perturbed Angular Correlations of -rays has been used to study the rotational correlation times in aqueous solution of the peptides: oxytocin, glycyltryptophan, cholecystokinin and the glycopeptide ristocetin. These peptides were labelled with excited ^111mCd through the covalent coupling of the metal chelator diethylenetriaminepentaacetic acid (DTPA) to the primary amines-of the peptides. The experimental correlation times are in good accordance with calculations based on the molecular weight. This indicates that the ^111mCd-DTPA is rigidly bound to the molecules. In the case of ristocetin, the correlation time was measured at 2°C, 25°C and 38°C. These experiments show the expected linear dependence on the viscosity divided by temperature. The feasibility of determining rotational correlation times for peptides without lysines and with correlation times in the ns region is thus demonstrated. Also, the correlation time of ^111mCd-DTPA coupled to the lysines of bovine serum albumin was determined. The measured correlation time is about 5 times less than the calculated correlation time. This effect is assigned to local motion. In spite of this, experiments show that ^111mCd-DTPA-bovine-serum-albumin is significantly immobilised by aggregation with immunoglobulins. The nuclear quadrupole interactions, necessary for determining the correlations times, were determined for ^111mCd-DTPA-ristocetin and ^111mCd-DTPA-bovine-serum-albumin by adding sucrose to a concentration of 63% and cooling to 2°C. This showed a small but significant difference between the two molecules. We interpret this as due to different conformations, possibly different coordination numbers. Offprint requests to: E. Danielsen     

Complete amino acid sequence of human intestinal aminopeptidase N as deduced from cloned cDNA

The complete primary structure (967 amino acids) of an intestinal human aminopeptidase N (EC 3.4.11.2) was deduced from the sequence of a cDNA clone. Aminopeptidase N is anchored to the microvillar membrane via an uncleaved signal for membrane insertion. A domain constituting amino acid 250-555 positioned within the catalytic domain shows very clear homology to E. coli aminopeptidase N and contains Zn2+ ligands. Therefore these residues are part of the active site. However, no homology of the anchor/junctional peptide domain is found suggesting that the juxta- and intra-membraneous parts of the molecule have been added/preserved during development. It is speculated that this part carries the apical address.     

Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex

The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S nuclear ribosomal DNA sequence and the intervening 5.8S region were sequenced from three individuals in each of eight taxa of the Mimulus guttatus species complex. Three discrete variants, or "types," of ITS sequences were found, among which 30%-40% of sites differed, compared with 1%-2% within types. Dot plots indicate that these types were not related by conspicuous rearrangements or inversions. More than one ITS type was often found in the same taxon, and two of three ITS types span species boundaries, indicating their presence prior to speciation. These ITS sequences showed essentially no positional homology with the nearest sequenced relative, tomato. In contrast, the 5.8S region was relatively unvaried, with 8 of 162 sites varied in the sample among all eight taxa. The phylogeny inferred by the most common ITS sequence type, rooted by the two other ITS types, agreed with isozymes in showing the distinctness of M. nudatus, M. laciniatus, and M. tilingii from the other five taxa.