Mutations affecting the enzymes involved in the utilization of 4-aminobutyric acid as nitrogen source by the yeast Saccharomyces cerevisiae

We present genetic evidence for the enzymes 4-aminobutyrate: 2-oxoglutarate aminotransferase (EC 2.6.1.19) and succinate-semialdehyde dehydrogenase [NAD(P)+] (EC 1.2.1.16) constituting the functional pathway for the utilization of 4-aminobutyric acid as a nitrogen source by Saccharomyces cerevisiae. We show that the pathway is induced by 4-aminobutyric acid and that the presence of the pathway enzymes probably requires the integrity of a positive control element.     

Rapid method for evaluating intra-erythrocyte Na+ activity

The measurements of intracellular "Na+ activity" was performed in 10 ml of heparinized venous blood. First the blood was three times washed in isotonic magnesium chloride solution (114 mmol/l). Thereby the buffy coat was removed. Then the microhematrocrit was taken for packet cell volume determination. After the erythrocytes were lysed by ultrasound. Sodium "Na+ Activity" is measured in the hemolysate by Ion-Selective electrode. With this method all "pipetting" operations are eliminated and for the "Na+ activity" determination was used ion-selective electrode with an indirect measurements, which is less influenced by the matrix. Reference intervals determined for a healthy population were 7.3 +/- 0.6 mmol/l.     

Molecular cloning of cDNA coding for human preprourokinase

A cDNA library was constructed in pBR322 from 18S to 20S mRNA that was extracted from human kidney cells, fractionated on oligo(dT)-cellulose column and sucrose-density gradient, and confirmed for urokinase production in Xenopus laevis oocytes. The Escherichia coli RR1 transformants were hybridized to synthetic oligonucleotide probe prepared according to the known amino acid sequence, Glu 73 to Glu 77 of human urinary urokinase chain B. The entire cloned cDNA covers a 2250-bp region, wherein the 1293-bp sequence codes for preprourokinase consisting of 431 amino acids, with the first 20 residues being a signal peptide. The 5'-untranslated region is at least 80 bp long and the 3'-untranslated region is longer than 850 bp.     

3H-uridine labelling patterns and chromosomal polymorphism inDrosophila subobscura: J and U chromosomes

The³H-uridine labelling patterns in J and U polytene chromosomes ofDrosophila subobscura were determined. The analysis was carried out in two developmental stages and in two strains proceeding from the same geographical origin whose genotypes were: J_st/J_st; U₁₊₂/U₁₊₂ and J₁/J₁; U₁₊₂₊₈/U₁₊₂₊₈ respectively. It was observed that the labelling pattern coincided very approximately with the puffing pattern in the same stages and chromosomal arrangements. Comparison of the³H-Uridine incorporation patterns between chromosomal arrangements showed light quantitative differences. These results are discussed in relation to the inversion effect.     

The thermodynamics of complex formation of cyclic tetra-aza-tetracetic acids

Enthalpy changes for the complexation of alkaline-earth and transition metals with three cyclic tetra-aza-tetracetic acids (cDOTA, cTRITA and cTETA) were obtained by continuous titration calorimetry. From these values and free energy data, the entropy changes for the same reactions were derived. The results show that these complexes are stabilised by both favourable enthalpy and entropy changes, except those of Mg²⁺ and those of Sr²⁺ and Ba²⁺ with cTETA. Generally, the entropy changes for the reactions of the alkaline-earth metals are higher than for the reactions of the non cyclic polyaminocarboxylic acids, but for the reactions of the transition metals the entropy changes are comparable for the cyclic and non cyclic ligands. These results are discussed in terms of a model of ‘cage’ coordination of the metals.The enthalpy changes decrease with the increase in size of the tetra-aza ring (except in the case of Cu²⁺) but no specific cavity size effect is noticeable. Consideration of the temperature-dependent and temperature-independent contributions to ΔH supports the idea that the number of coordinated nitrogen atoms and carboxylate groups vary along the series.     

The role of iron in the growth of human leukemic cell lines

The growth requirements of three human leukemic cell lines (K 562, HEL, U937) have been studied in the absence of serum. For growth in serum-free medium, the cells require insulin, transferrin, and albumin. Two highly water-soluble iron salts, ferric ammonium citrate and ferric ammonium sulfate, may completely replace transferrin for supporting the growth of these cell lines. Similar results were obtained when mitogen-stimulated lymphocytes were grown in serum-free media. Iron containing compounds, such as hemin or hemoglobin, were also able to replace transferrin. Experiments using 42/6 monoclonal antibody strongly suggest that free-iron salts are taken up by the cells by a mechanism that is completely independent from transferrin-receptors.     

Extracellular glucose-producing exodextranase of the yeast Lipomyces lipofer

A dextran-hydrolysing enzyme from Lipomyces lipofer IGC 4042 was purified from the supernatant of cultures grown on a mineral medium with dextran, by ultrafiltration and gel filtration on Bio Gel A-0.5 m. This preparation gave only one band by disc gel electrophoresis. Glucose was the only product of dextran hydrolysis. Optimum pH and temperature for the activity of the enzyme were pH 4.5–5.0 and 45°C, respectively. The enzyme was most stable over a pH range of 4.5–6.0, and after 2 hours at 50°C maintained over 60% of its original activity. The molecular weight was 29,000 daltons and the isoelectric point was at pH 7. K_m (45°C, pH 5) for dextran T-40 was 1.2×10^–5 M. Glucose inhibited the enzyme competitively with a K_i (45°C, pH 5) of 0.5 mM.