Human deoxyuridine triphosphate nucleotidohydrolase. Purification and characterization of the deoxyuridine triphosphate nucleotidohydrolase from acute lymphocytic leukemia

A new fast assay procedure for increasing deoxyuridine triphosphate nucleotidohydrolase activity was developed. With this assay procedure, this enzyme derived from blast cells of patients with acute lymphocytic leukemia was purified at least 1218-fold. The molecular weight was estimated by gel filtration to be 43,000. The enzyme exhibited optimal activity over a pH range of 7 to 8 and the activation energy was estimated to be 6.5 kcal/mol at pH 7.5. While the enzyme had activity in the absence of added divalent cations, the activity could be inhibited by EDTA but not by phenanthroline. The inhibition caused by EDTA could be reversed by Mg2+ or Zn2+. The enzyme had maximal activity in the presence of Mg2+ (40 muM) and Mg2+ (4 mM) stabilized the enzyme at 37 degrees C. Cupric ion (0.5 mM) inhibited (50%) enzyme activity in the presence or absence of Mg2+. The substrate for the enzyme was dUTP and the apparent Km was 1 muM. No other deoxyribonucleoside or ribonucleoside triphosphate served as a substrate for the enzyme.

Quantitative analysis of tubulin and microtubule compartments in isolated rat hepatocytes

A combined morphometric and biochemical approach has been used to identify and quantitate microtubules and tubulin in isolated hepatocytes. The total soluble pool of microtubule protein was estimated by specific high affinity binding to radiolabeled colchicine. Scatchard analysis of the data identified two populations of binding sites: high affinity-low capacity sites resembling tubulin and low affinity-high capacity sites believed to represent nonspecific colchicine-binding sites. Data from these studies indicate that tubulin represents 1% of the soluble protein of the cell, that 9.0 X 10(-14) dimers of tubulin are present per microgram soluble hepatocyte protein, and that the average hepatocyte contains 3.1 X 10(7) tubulin dimers. Our calculations suggest that this amount of tubulin would form a microtubule 1.9 cm in length if totally assembled. However, stereological measurements indicate that the actual length of microtubules in the cytosolic compartment of the average hepatocyte is only 0.28 cm. Thus, these experiments suggest that only 15% of the available tubulin in hepatocytes of postabsorptive rats is assembled in the form of microtubules.

Human thymidylate kinase. Purification, characterization, and kinetic behavior of the thymidylate kinase derived from chronic myelocytic leukemia

Thymidylate kinase derived from the blast cells of human chronic myelocytic leukemia was purified 2186-fold to near homogeneity by means of alcohol precipitation, alumina-Cgamma gel fractionation, calcium phosphate gel fraction, ultrafiltration, and affinity column chromatography. The molecular weight was estimated by glycerol gradient centrifugation to be 50,000. This enzyme had an optimal activity at pH 7.1 and required a divalent cation in order to catalyze the reaction. Mg2+ and Mn2+ were found to be the preferential divalent cations. The activation energy was estimated to be 19.1 kcal/mol at pH 7.2. Initial velocity study suggested that the reaction followed a sequential mechanism. Mg2+ ATP had a Km of 0.25 mM and dTMP had a Km of 40 micrometer. The enzyme was unstable even at 4 degrees. In the presence of ATP or dTMP the enzyme maintained its activity. Purine triphosphate nucleosides were found to be better phosphate donors than the pyrimidine triphosphate nucleosides. ATP and dATP had a lower Km and a higher Vmax than GTP and dGTP. dTMP was the only preferred phosphate receptor among all the monophosphate nucleotides tested dTTP and IdUTP competed with both substrates and inhibited the reaction with a Ki of 0.75 mM and 1.1 mM, respectively.

Partially miscible liquid systems: The density, change of volume on mixing, vapor pressure, surface tension, and viscosity in the system: aniline–hexane

The following properties have been investigated experimentally: density, change of volume on mixing, vapor pressure, surface tension, and viscosity, at temperatures above and below the critical solution temperature. The question at issue is: How does the chemical potential, or any property dependent on chemical potential, change, at constant temperature, over a range of composition, just above the critical solution temperature? In the present case, the vapor pressure and surface tension, properties directly dependent on chemical potential, are constant within the range of experimental accuracy (which, however, may not be sufficient) over a range of concentration. The viscosity is complicated by the occurrence of anomalous viscosity. The change of volume on mixing is negative, and this is usually associated with compound formation. In all other systems investigated by us, except the system triethylamine–water, ΔV is positive. We have shown elsewhere, however, that a very stable chemical compound is formed between water and triethylamine.