Desulfurization of model and diesel oils by resting cells of Gordona sp.

The desulfurization activity of the resting cells of Gordona sp. CYKS1 was strongly depended on harvest time and the highest value when the cells had been harvested in the early growth phase (0.12 mg sulfur g^–1 cell^–1 h^–1). For the model oil, hexadecane containing dibenzothiophene, the specific desulfurization rate decreased as the reaction proceeded. Both the specific and the volumetric desulfurization rates were not significantly affected by the aqueous-to-oil phase ratio. The diesel oils, light gas oil and a middle distillate unit feed were desulfurized at higher rates (ca. 0.34 mg sulfur g^–1 cell^–1 h^–1) than the model oil (0.12 mg sulfur g^–1 cell^–1 h^–1).     

Enhancement of cell growth by intracellularly expressed herpes simplex virus thymidine kinase

A recombinant cell line (NIH3T3:pLtkSN) was made by infecting parental cells (NIH3T3) with a recombinant retrovirus (pLtkSN) encoding herpes simplex virus thymidine kinase (HSVtk) gene. The cells expressing HSVtk (NIH3T3:pLtkSN) grew 2.3 times more than the parental cells (NIH3T3) in Dulbecco's Modified Eagles Media containing 10% (v/v) horse serum. The NIH3T3:pLtkSN cells also showed a significant enhancement in the maximal cell concentration and the specific growth rate even at 2.5% serum concentration. The specific O2 uptake rate of NIH3T3 was 2.1 times greater than that of NIH3T3:pLtkSN. Under both O2-limited and O2-unlimited conditions, it appears that HSVtk plays an important role in enhancing the growth characteristics of animal cells.     

Specificity and non-specificity of synaptic connections within mammalian visual cortex

It is clear from reviewing the findings of our own studies and those of others that the cerebral cortex has combined two very different strategies of organisation. Firstly it has a strictly defined genetically determined substrate of specific neurons classes, specific rules for which kinds of cells interconnect, a laminar architecture where efferent and afferent relays and interlaminar links are predetermined. But, as well, a second strategy allows great developmental lability in the precise spatial patterns of intralaminar circuits of the excitatory neurons and in the actual weights of excitatory and inhibitory synapses that are contributed to each neuron. This second strategy presumably allows the cortex to be tailor-made to the early experience of each individual and, as well, allow for lability of responses to different conditions of stimulation and adjustment of the system to compensate to some degree for injuries affecting afferents and circuitry in the adult system.     

Genome-wide CRISPR Screens Reveal Host Factors Critical for SARS-CoV-2 Infection

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Efficient use and recycling of the micronutrient iodide in mammals

Daily ingestion of iodide alone is not adequate to sustain production of the thyroid hormones, tri- and tetraiodothyronine. Proper maintenance of iodide in vivo also requires its active transport into the thyroid and its salvage from mono- and diiodotyrosine that are formed in excess during hormone biosynthesis. The enzyme iodotyrosine deiodinase responsible for this salvage is unusual in its ability to catalyze a reductive dehalogenation reaction dependent on a flavin cofactor, FMN. Initial characterization of this enzyme was limited by its membrane association, difficult purification and poor stability. The deiodinase became amenable to detailed analysis only after identification and heterologous expression of its gene. Site-directed mutagenesis recently demonstrated that cysteine residues are not necessary for enzymatic activity in contrast to precedence set by other reductive dehalogenases. Truncation of the N-terminal membrane anchor of the deiodinase has provided a soluble and stable source of enzyme sufficient for crystallographic studies. The structure of an enzyme·substrate co-crystal has become invaluable for understanding the origins of substrate selectivity and the mutations causing thyroid disease in humans.     

Regulation of G(1) cell-cycle progression by oncogenes and tumor suppressor genes.

Progression of resting quiescent G(0) cells into early G(1) and transition across the restriction point are highly regulated processes. Mutation of proto-oncogenes and tumor suppressor genes regulating these transitions are targeted during oncogenesis. Recent work has underscored the importance of the G(0) to early G(1) transition and metabolism to neoplastic cells.     

Human beta-glucuronidase. Studies on the effects of pH and bile acids in regard to its role in the pathogenesis of cholelithiasis

Human bile contains a considerable amount of endogenous beta-glucuronidase. The effects of pH and bile acids on its activity have been studied in regard to its role in the pathogenesis of cholelithiasis. beta-Glucuronidase, purified from human liver to homogeneity, was structurally stable between pH 4 and 10, but was active only over a much narrower range of pH, with a pH optimum of 5.2. The inactivation below pH 4 was due to its irreversible denaturation, whereas the inactivation at higher pH was due to a true reversible pH effect on the enzyme velocity. Kinetic studies revealed that hydrogen ion acted as a substrate-directed activator of the free enzyme, but not the enzyme-substrate complex, with a molecular dissociation constant of 4 X 10(-6). The enzyme activity was not affected by unconjugated bile acids, primarily due to their extremely low water solubility. Conjugated bile acids, on the other hand, exerted heterogeneous and pH-dependent effects on the enzyme. At pH 5.2, taurocholic acid and glycocholic acid were substrate-directed activators of the enzyme; taurochenodeoxycholic acid and taurodeoxycholic acid, competitive inhibitors; and glycochenodeoxycholic acid and glycodeoxycholic acid, mixed inhibitors. At pH 7.0 all taurine and glycine conjugates behaved as substrate-directed activators. Though beta-glucuronidase activity at pH 7 was only 23% of its maximal activity at pH 5.2, conjugated bile acids tended to restore its activity to a certain extent at pH 7. Thus, endogenous beta-glucuronidase could play a significant role in pigment cholelithiasis.