Formation of tyrosine from glycine, formaldehyde and phenol under the action of a partially purified preparation of tyrosine phenol lyase: The participation of a different enzyme

In the presence of a partially purified preparation of tyrosine phenol lyase, tyrosine is formed in solutions containing glycine, formaldehyde and phenol. The enzyme preparation also catalysed the splitting of allothreonine to glycine and acetaldehyde. An enzyme which is different from tyrosine phenol lyase was shown to be responsible for this aldolase reaction. When an enzyme preparation with a higher specific activity of tyrosine phenol lyase, but without aldolase activity, was used the formation of tyrosine from glycine, formaldehyde and phenol was not observed. It is assumed that the first stage of the process is the formation of serine from glycine and formaldehyde catalysed by the enzyme responsible for the aldolase reaction. Serine in its turn is converted to tyrosine by tyrosine phenol lyase.     

Immunoenzyme determination of antibodies to the surface of islands of Langerhans in autoimmune destruction of the insular apparatus

Enzyme-linked immunosorbent assay (ELISA) was applied for detection of human islet cell surface antibodies (ICSA) to rat islet target cells. In 23 healthy controls without hereditary diabetes the findings were on the upper normal limit (mean value of optical density + 3 SEM). The results above the limit were considered positive. 11 out of 18 insulin-dependent (Type I) diabetics with the disease duration less than 5 years were ICSA-positive. All 9 patients with insulin-independent (Type 2) diabetes were ICSA-negative. 3 out of 18 healthy subjects (siblings and children of probands with type II diabetes) were strongly ICSA-positive, although all the members of this risk group had unimpaired oral glucose tolerance test. Thus, ELISA screening of ICSA may be useful for discriminating patients with different types of diabetes and revealing nonaffected individuals at high risk according to their beta-cell integrity.     

The Ultuna long-term soil organic matter experiment

In 1991, soil samples were taken from the long-term (40 years old) field trial at Ultuna in order to investigate soil P status and the distribution of its various forms. Among the treatments investigated, two were inorganic PK additions only – one to continuous fallow (PK-fallow) and the other to cropped fields (PK). There were also treatments amended with PK in combination with applications of straw, green manure composed of grass (GM), farmyard manure (FYM) or sewage sludge (SS). A total of 720, 720, 883, 1154, 1941 and 6617 kg P h^-1 had been supplied in the PK-fallow, PK, Straw, GM, FYM and SS treatments, respectively up to 1991. The soil P distribution was determined by step-wise fractionation using anion exchange resin (resin-P), sodium bicarbonate (bicarb-P), sodium hydroxide (hyd-P), and HCl (HCl-P). Finally, the soil was digested to obtain residual P (resid-P). The amendments resulted in a significant (p=0.05) enrichment of total P in soils relative to the initial value. A breakdown of the bicarb-P and hyd-P into inorganic P (P_i) and organic P (P_o) was manifested as considerable transformations within these P compartments compared with the initial values. Thus, total P_i (resin-P, bicarb-P_i, hyd-P_i, HC1-P, resid-P)/total P_o (bicarb-P_o, hyd-P_o) ratios markedly decreased in all treatments relative to control. The two P compartments were significantly and negatively (p =0.05) correlated. On average, the total P_o increase was about 380 mg kg^-1 (range 270–715). The results suggested that an equilibrium between P_i immobilization and P_o mineralization was difficult to attain under any of the experimental management regimes used, which exclude inorganic N application. The balance sheet calculations revealed P deficits ranging from about 10 to 60 kg ha^-1, indicating that some P had migrated to the subsoil.     

Catalytic properties of extracts from tyrosine phenol lyase producing cells of Escherichia intermedia: Multienzyme complex instead of the single multisubstrate enzyme

Kinetic parameters for the formation of pyruvate from L-tyrosine catalysed by the cell extract of Escherichia intermedia A-21 differ markedly from the parameters of crystalline tyrosine phenol lyase taken from the literature. The substrate specificity of the enzyme in the cell extract was also found to be different from that in the crystalline state. The cell extracts did not show any activity with respect to D-tyrosine, while the reactions with L-and D-enantiomers of serine were brought about mainly by active sites which differ kinetically from the active site responsible for the main reaction. The ratio of activities with respect to L-tyrosine, L-serine and D-serine varied widely depending on the composition of the medium on which the cells had been grown. The high activity of the preparation with respect to L-tyrosine is not a sufficient condition for successful tyrosine synthesis from dl-serine. High activities towards serine enantiomers are also necessary.     

Responses of Azospirillum brasilense to Nitrogen Deficiency and to Wheat Lectin: A Diffuse Reflectance Infrared Fourier Transform (DRIFT) Spectroscopic Study

For the rhizobacterium Azospirillum brasilense, the optimal nutritional range of C:N ratios corresponds to the presence of malate (ca. 3 to 5 g l⁻¹ of its sodium salt) and ammonium (ca. 0.5 to 3 g l⁻¹ of NH₄Cl) as preferred carbon and nitrogen sources, respectively. This microaerophilic aerotactic bacterium is known to have a narrow optimal oxygen concentration range of ca. 3 to 5 μM, which is 1.2% to 2% of oxygen solubility in air-saturated water under normal conditions. In this work, the effects of stress conditions (bound-nitrogen deficiency related to a high C:N ratio in the medium; excess of oxygen) on aerobically grown A. brasilense Sp245, a native wheat-associated endophyte, were investigated in the absence and presence of wheat germ agglutinin (WGA, plant stress protein and a molecular host-plant signal for the bacterium) using FTIR spectroscopy of whole cells in the diffuse reflectance mode (DRIFT). The nutritional stress resulted in the appearance of prominent spectroscopic signs of poly-3-hydroxybutyrate (PHB) accumulation in the bacterial cells; in addition, splitting of the amide I band related to bacterial cellular proteins indicated some stress-induced alterations in their secondary structure components. Similar structural changes were observed in the presence of nanomolar WGA both in stressed A. brasilense cells and under normal nutritional conditions. Comparative analysis of the data obtained and the relevant literature data indicated that the stress conditions applied (which resulted in the accumulation of PHB involved in stress tolerance) and/or the presence of nanomolar concentrations of WGA induced synthesis of bacterial cell-surface (glyco)proteins rich in β-structures, that could be represented by hemagglutinin and/or porin.     

The precursor hematopoietic cell: its origin in ontogeny, proliferative activity and proliferative potential

Cells responsible for repopulation of irradiated longterm cultures of murine bone marrow and capable of generating CFUs for at least 4-5 weeks after seeding referred here to as primitive hemopoietic stem cells (P-HSC) were assayed by limiting dilution analysis. During development of mice P-HSC can be detected for the first time in the liver of 12-13-day-old embryos and their number is about 10 per organ. At day 17-18 of gestation the number of P-HSC increases ten-fold; however, we could not detect the proliferation of these cells using the technique of hydroxyurea suicide. In the adult mouse P-HSC content is about 100 precursors per femur and their concentration is one P-HSC per 1-2 x 10(5) bone marrow cells. P-HSC content in the spleen is 0.5 per 10(6) cells. In vivo treatment with 5-fluorouracil or hydroxyurea (six injections every 6 h) does not alter significantly the number of P-HSC, although either treatment kills about 99% of CFUs. Several months after reconstitution of lethally irradiated mice with a "small" inoculum of bone marrow cells (0.20-0.35 x 10(6)) the number of bone marrow P-HSC was reduced as compared to that in animals reconstituted by injection of a "large" cell dose (20-35 x 10(6)). These data suggest that P-HSC have limited proliferative potential and are incapable of self-maintenance.