Three-dimensional structure of a mutant ribonuclease T1 (Y45W) complexed with non-cognizable ribonucleotide, 2'AMP, and its comparison with a specific complex with 2'GMP.

The crystal structure of a mutant ribonuclease T1 (Y45W) complexed with a non-cognizable ribonucleotide, 2'AMP, has been determined and refined to an R-factor of 0.159 using X-ray diffraction data at 1.7 A resolution. A specific complex of the enzyme with 2'GMP was also determined and refined to an R-factor of 0.173 at 1.9 A resolution. The adenine base of 2'AMP was found at a base-binding site that is far apart from the guanine recognition site, where the guanine base of 2'GMP binds. The binding of the adenine base is mediated by a single hydrogen bond and stacking interaction of the base with the imidazole ring of His92. The mode of stacking of the adenine base with His92 is similar to the stacking of the guanine base observed in complexes of ribonuclease T1 with guanylyl-2',5'-guanosine, reported by Koepke et al., and two guanosine bases, reported by Lenz et al., and in the complex of barnase with d(GpC), reported by Baudet & Janin. These observations suggest that the site is non-specific for base binding. The phosphate group of 2'AMP is tightly locked at the catalytic site with seven hydrogen bonds to the enzyme in a similar manner to that of 2'GMP. In addition, two hydrogen bonds are formed between the sugar moiety of 2'AMP and the enzyme. The 2'AMP molecule adopts the anti conformation of the glycosidic bond and C-3'-exo sugar pucker, whereas 2'GMP is in the syn conformation with C-3'-endo-C'-2'-exo pucker. The mutation enhances the binding of 2'GMP with conformational changes of the sugar ring and displacement of the phosphate group towards the interior of the catalytic site from the corresponding position in the wild-type enzyme complex. Comparison of two crystal structures obtained provides a solution to the problem that non-cognizable nucleotides exhibit unexpectedly strong binding to the enzyme, compared with high specificity in nucleolytic activity. The results indicate that the discrimination of the guanine base from the other nucleotide bases at the guanine recognition site is more effective than that estimated from nucleotide-binding experiments so far.     

A lymphocyte blastogenesis inhibitory factor (LBIF) reversibly arrests a human melanoma cell line, A375, at G1 and G2 phases of cell cycle

A lymphocyte blastogenesis inhibitory factor, LBIF, has been found in the culture supernatant of a human macrophage-like cell line, U937. The factor has been purified by fast protein liquid chromatography. Partial amino acid sequencing analysis showed that LBIF was a novel immunoregulatory factor. Recent study has demonstrated that LBIF possesses a remarkable tumor growth inhibitory activity. In this study, the cell growth inhibitory activity of LBIF was characterized on the proliferation of a human melanoma cell line A375 in vitro. LBIF strongly inhibits the proliferation of A375 cells. The inhibitory activity was cytostatic and reversible by Day 5 although the lethal effect became apparent at Day 7. Cell cycle analysis by flow cytometry showed that LBIF arrested A375 cells at both G₁ and G₂/M phases. Mitotic index analysis indicated that A375 cells were arrested in G₁ and G₂ phases. LBIF function was not attributed to the elevation of intracytoplasmic cyclic-AMP levels. Thus, these results suggest that LBIF plays an important role in controlling cell cycle and there is a similarity between the mechanisms of G₁ and G₂ arrests in eukaryotic cell proliferation. LBIF-induced reversible cell-cycle arrest of A375 cells can be a useful system to analyze the signal transduction for cell proliferation and cell-cycle arrest.     

Production of Coenzyme A by Sarcina lutea

To develop an efficient method for the production of coenzyme A (CoA), optimal conditions for its formation from pantothenic acid, cysteine, and adenine were studied. A number of microorganisms were screened for production of CoA. Strains belonging to the genera Sarcina, Bacillus, Microbacterium, Micrococcus, and Serratia accumulated CoA. Among these, Sarcina lutea was selected as the best organism, and the culture conditions for the production of CoA were investigated with this organism. Under optimal conditions, 600 mug of CoA per ml was accumulated in the culture broth. CoA was readily isolated in high purity by the use of charcoal, diethylaminoethyl-cellulose, Sephadex G-25, and Dowex-50. Yields of isolated CoA were over 33% from culture broth.     

Production of Flavine-Adenine Dinucleotide from Riboflavine by a Mutant of Sarcina lutea

A study was made to develop a new method for the production of flavine-adenine dinucleotide (FAD) from riboflavine and adenine by a mutant of Sarcina lutea deficient in the enzyme adenosine deaminase. It was found that this strain could convert exogenously supplemented riboflavine to extracellular FAD. The yields of FAD were increased by addition of D-cycloserine in the culture medium. The culture conditions for FAD production were investigated under the addition of D-cycloserine, and increased production of FAD was observed with the addition of an appropriate amount of thiamine, acetate, and sodium ion. The yield of 0.7 g/liter was obtained in the optimal culture in 5 days. Accumulated FAD was readily isolated by adsorption chromatography and ion-exchange chromatography in a 70% yield.     

Effects of thiamine and pyridoxine on the content and composition of sterols in Saccharomyces carlsbergensis 4228

The level of sterols in $\text{S. carlsbergensis}$ 4228 cells grown aerobically on a synthetic medium fortified with thiamine was significantly low compared with that in the control cells. The levels of free and esterified sterols in the thiamine-cells were 60% and 10% of the corresponding sterol levels in the control cells, respectively. Analysis by gas-liquid chromatography of non-saponifiable lipids extracted from the cells revealed that the amounts of squalene, lanosterol and two unidentified sterols were higher than those in the control cells and that ergosterol and zymosterol, major sterols in the control cells, were not present. These effects of thiamine on the content and composition of sterols were abolished by the addition of pyridoxine to the medium.     

Biological actions of peptide YY: effects on endocrine pancreas, pituitary-adrenal axis, and plasma catecholamine concentrations in the dog

The present study was designed to gather information on the biological activity of peptide YY (PYY) in conscious dogs. PYY was infused intravenously at a dose of 238 pmol/kg X h, and plasma concentrations of glucose, insulin, pancreatic polypeptide (PP), ACTH, cortisol and catecholamines (norepinephrine-NE; epinephrine-E; dopamine-DA) were subsequently measured. PYY significantly increased plasma insulin levels transiently without effect on plasma glucose, but decreased plasma PP levels during all infusion periods. PYY stimulated both plasma ACTH and cortisol secretion, and this action of PYY was also shared by PP, with PP being less potent in ACTH-cortisol release. PYY further elicited specific changes in plasma catecholamine concentrations, i.e. an increase of NE but not of E, which were in contrast to the effects of insulin-induced hypoglycemia. PP failed to alter plasma insulin and catecholamine concentrations. These results suggest that PYY can affect anterior pituitary hormone secretion, sympathetic nervous outflow and pancreatic endocrine activity in addition to its known actions on gastric and pancreatic secretion in the dog.     

Human epidermal plasminogen activator : Characterization, localization, and modulation

Using biochemical and immunocytochemical approaches, we have investigated the plasminogen activator (PA) of primary human epidermal cell cultures. A rabbit antibody raised against human urinary PA (urokinase) inhibited greater than or equal to 96% of the PA activity in the keratinocyte cultures. Immunoblot and double immunodiffusion analyses of keratinocyte PA with anti-urokinase antibody confirmed that epidermal PA was of the urokinase type. Immunocytochemical investigation of human keratinocyte cultures with anti-urokinase antibody revealed two characteristic staining patterns for PA. First, cells at the advancing edge of subconfluent colonies were cytoplasmically stained in a granular pattern. Similar staining was observed at the migrating edges of confluent epidermal cell cultures that had been wounded by cutting with a blade. This induction of PA staining was independent of cell division. Secondly, differentiated epidermal cells located on the surface of colonies were stained either at the plasma membrane or homogeneously throughout the cell. The highly differentiated, spontaneously shed cells were usually very heavily stained by anti-urokinase antibody. These immunocytochemical experiments suggest that PA expression is highly regulated in human epidermal cells. Specifically, PA expression appears to be related to cellular differentiation and to cell movement in expanding or wounded keratinocyte colonies.