Partial characterization of microsomal sialyltransferase from chicken liver and hepatoma Mc-29: I. Effect of nucleotides and metal ions

CMP-N-acetylneuraminic acid: glycoprotein sialyltransferase activities were assayed in microsomal fractions from chicken liver and hepatoma, induced by the leukosis virus strain Mc-29, using asialofetuin as the substrate acceptor of N-acetylneuraminic acid. The effect of some nucleotides and metal ions on the enzyme activity was investigated. Kinetic studies revealed that the Km values toward asialofetuin at a saturation concentrations of CMP-N-acetylneuraminic acid for both liver and hepatoma enzymes are very closed, while V value was lower for the tumor enzyme. The liver and hepatoma enzymes have no exogenous Mn cations requirement and are inhibited by CTP, CMP and ATP. CMP was shown to act as a competitive inhibitor with an apparent Ki of 0.24 mM for the liver and 0.16 mM for hepatoma enzyme, respectively.     

The study of nucleoside triphosphate-binding center of DNA-dependent RNA-polymerase of phage T7 using GTP analogs

The NTP binding site of bacteriophage T7 DNA-dependent RNA polymerase was studied using GTP analogs. For four analogs the irreversible inhibition was demonstrated. The kinetic parameters for competitive (Ki) and irreversible (KI and k3) inhibition were determined. One of the analogs, 5'[2-hydroxy(4-iodoacetamido)benzoyl]guanosine, was shown to inactivate the enzyme rapidly due to the modification of SH-groups. Some suggestions on the structure of the RNA polymerase active site have been made.     

Evidence for direct arrhythmogenic action of endothelin.

We studied electrophysiological effects of endothelin on canine cardiac tissues. Endothelin prolonged action potential duration and decreased spontaneous firing rate of the right bundle branch cells. At a concentration of 2 x 10(-7)M the plateau phase of action potentials was flattened, followed by the abrupt occurrence of early afterdepolarizations (EADs). ET, at a concentration as low as 2 x 10(-9)M, was capable of inducing EADs although their incidence was low. The EADs were initiated from the membrane potential less negative than -30mV and were suppressed by nicardipine, suggesting the involvement of dihydropyridine-sensitive Ca2+ channels in the induction of EADs. Because EADs are considered to underlie certain types of arrhythmias endothelin per se may have arrhythmogenic action.     

Measurement of active-site homology between potato and rabbit muscle alpha-glucan phosphorylases through use of a linear free energy relationship

The Michaelis-Menten parameters (Vmax and Km) for turnover of an extensive series of deoxy and deoxyfluoro derivatives of alpha-D-glucopyranosyl phosphate by the alpha-glucan phosphorylase from potato tuber have been determined. Very large rate reductions are observed as a consequence of each substitution, primarily due to losses in specific binding interactions, most likely hydrogen bonding, at the enzymic transition state. Comparison of the Vmax/Km values so determined with those measured for rabbit muscle alpha-glucan phosphorylase [Street et al. (1989) Biochemistry 28, 1581] reveals an astonishingly similar specificity, especially in light of the phylogenetic separation of their host organisms. This indicates that very similar hydrogen-bonding interactions between the enzyme and the substrate must be present at the transition states for the two enzymic reactions; therefore, they have very similar active sites. Quantitation of this similarity is achieved by plotting the logarithm of the Vmax/Km value for each substrate analogue with the potato enzyme against the same parameter for the muscle enzyme, yielding straight lines (p = 0.998 and 0.999) of slope 1.0 and 1.2 for the deoxy and deoxyfluoro substrates, respectively. Since the correlation coefficient of such plots is a direct measure of the similarity of the two transition-state complexes, thus of the enzyme active sites, it can be used as a measure of active-site homology between the two enzymes. The extremely high homology observed in this case is consistent with the observed sequence homology at the active site.     

Phylogenetic analysis and secondary structure of the Bacillus subtilis bacteriophage RNA required for DNA packaging

An unusual RNA molecule encoded by the Bacillus subtilis bacteriophage phi 29 is a structural component of the viral prohead and is required for the ATP-dependent packaging of DNA. Here we report a model of secondary structure for this prohead RNA developed from a phylogenetic analysis of the primary sequences of prohead RNAs of related phages. Twenty-nine phages related to phi 29 were found to produce prohead RNAs. These RNAs were analyzed by their ability to replace phi 29 RNA in in vitro phage assembly, by Northern blot hybridization with a probe complementary to phi 29 RNA, and by partial and complete sequence analyses. These analyses revealed four quite different sequences ranging in length from 161 to 174 residues. The secondary structure deduced from these sequences, in agreement with earlier observations, indicated that prohead RNA is organized into two domains. The larger 5'-domain (Domain I) is composed of 113-117 residues and contains four helices. Three of these helices appear to be organized into a central stem that is interrupted by two unpaired loops and the fourth helix and loop. The smaller 3'-domain (Domain II) is composed of 40-44 residues and consists of two helices. Domains I and II are separated by 8-13 unpaired residues. Nuclease cleavage occurs readily in this single-stranded joining region, and this cleavage allows the subsequent separation of the two RNA domains. The separated Domain I is fully active in DNA packaging in vitro. The functional significance and biological role of Domain II are unknown. The phylogenetic secondary structure model provides a basis for further analysis of the role of this RNA in bacteriophage morphogenesis.     

Localization of adherens junction proteins along the possible sliding interface between secretory ameloblasts of the rat incisor

Localization of junctions between inner enamel-secretory ameloblasts was examined by immunofluorescence microscopy using antibodies against adherens junction proteins, radixin, vinculin, and A-CAM. All antibodies used stained the boundary between the ameloblasts exclusively in the plane where F-actin was abundant. This suggests that the adherens junctions in the ameloblasts are involved in cell-to-cell movement with actin-based microfilament bundles.     

The quantitative analysis of lipopolysaccharide antigen in the blood serum of patients with salmonellosis by using complement-bound liposome lysis]

Titration of group B Salmonella O-antigen in the blood sera of patients and donors was carried out by means of the complement-dependent lysis of liposomes sensitized with S. typhimurium LPS. Good correlation (r = 0.95) of the levels of S. typhimurium somatic O-antigen in the patients' sera determined by liposomal immunoassay and aggregate hemagglutination test was established. The concentration of the antigens in the tested samples was within 0.5-50 micrograms/ml. Statistical analysis of the results obtained by liposomal immunoassay techniques demonstrated differences in the distribution functions for the blood sera of patients with different diseases and of donors.     

Effect of mastectomy versus mastectomy plus adjuvant ovariectomy on prolactin response to TRH in breast cancer

The endocrine effects of ovariectomy need to be further investigated. The present study was carried out to evaluate the influence of the adjuvant ovariectomy on the mastectomy-induced changes in PRL response to TRH in breast cancer. The study included 34 patients with locally limited breast carcinoma, 18 of whom were treated with radical mastectomy, whereas the other 16 underwent mastectomy plus adjuvant ovariectomy. PRL secretion in response to TRH (200 mcg I.V. as bolus) was evaluated one day before and 7 days after surgery. In patients treated with mastectomy only, PRL increase after TRH was significantly higher after surgery than before. On the contrary, no difference was seen in patients treated with mastectomy plus ovariectomy. This study shows that the adjuvant ovariectomy may block the increase in PRL response to TRH induced by mastectomy in breast cancer.