5-Azidoindole binding to the Escherichia coli tryptophan synthase alpha 2 beta 2 complex

The tryptophan synthase alpha 2 beta 2 complex catalyzes tryptophan (Trp) biosynthesis from serine plus either indole (IN) or indole-3-glycerol phosphate (InGP). The photoreactive 5-azido analog in IN (AzIN), itself a substrate in the dark, was utilized to examine the substrate binding sites on this enzyme. When irradiated with AzIN at concentrations approaching IN saturation for the IN----Trp activity (0.1 mM), in the absence of serine, the enzyme was increasingly inactivated (up to 70-80%) concomitant with the progressive binding of a net of 2 mol AzIN per alpha beta equivalent. Little or no cooperativity in the binding of the 2 mol AzIN was observed. In contrast, there was minimal effect on the IN----InGP activity. Under these conditions AzIN appeared to be incorporated equally into each subunit. No significant inactivation nor binding occurred in the presence of serine. A quantitatively similar inactivation of InGP----Trp activity was observed over the same AzIN concentration range, suggesting common IN sites for Trp biosynthesis from either indole substrate. At higher concentrations (0.1-0.7 mM), no further inactivation occurred, although there was extensive additional binding (up to 10 mol/alpha beta equivalent). These data are consistent, although more clear-cut quantitatively, with the high- and low-affinity sites proposed from equilibrium dialysis studies. AzIN binding studies utilizing the isolated beta 2 subunit confirmed earlier reports suggesting the existence of many nonspecific IN binding sites on this subunit.     

The photosensitizing activity of haematoporphyrin on mollicutes

The photosensitizing activity of haematoporphyrin (HP) on Mycoplasma hominis and Acholeplasma laidlawii was studied as a function of the phase of growth and the amount of sterols in the cell membrane. Less HP was bound to cells when the membrane had a high sterol content. Both strains in the exponential but not in the stationary phase of growth were sensitive to HP treatment (above 1 microgram ml-1) in the dark. Visible light irradiation of HP-loaded cells caused in all cases a decrease of cell survival, with concomitant changes in the pattern of membrane proteins that suggested protein-protein cross-linking, and the appearance of ultrastructural alterations (rounded and lysed cells); the photosensitivity was indirectly related to the sterol content of the cell membrane. On the whole, our findings suggest that the cell membrane is a major target for HP photosensitization of mycoplasma cells.     

Effect of substrate structure on the pre-steady-state kinetics of oxidation by liver alcohol dehydrogenase. A correlation with the Taft sigma parameter.

The oxidation of a series of primary alcohols by liver alcohol dehydrogenase has been studied under conditions of [S]o greater than [E]o using the stopped-flow method. A biphasic process, with exponential rise to a steady state, was observed for most of the alcohols and the rate constants for the transient phase were determined. No transient phase could be detected for 2-chloroethanol and 2-nitroethanol and steady-state measurements were made for these alcohols. The rate constants for the hydrogen transfer step were obtained from the pre-steady-state rate constants for the various alcohols and correlated with the Taft sigma constant. The (see article) value obtained (-1.8) is consistent with rate-limiting hydride transfer coupled with removal of the hydroxyl proton by a suitable basic group on the enzyme. A possible identity for this group is suggested.     

No association of moon phase with stroke occurrence

Stroke occurrence shows strong correlations with sleep disorders and even subtle sleep disturbances have been shown to affect ischemic stroke (IS) occurrence. Chronobiology also exerts effects, like the morning surge in IS occurrence. Lunar cycles have also been shown to affect sleep and other physiological processes, but studies on moon phases and its possible association with occurrence of stroke are rare and nonconclusive. Therefore, we studied the effects of moon phases on stroke hospitalizations and in-hospital mortality nationwide in Finland in 2004–2014. All patients aged ≥18 years with IS or intracerebral hemorrhage (ICH) as primary discharge diagnosis were included. Daily number of admissions was treated as a response variable while moon phase, year and astronomical season were independent variables in Poisson regression modeling. We found no association between moon phases and stroke occurrence. The overall occurrence rates did not vary between different moon phases for IS or ICH (p = 0.61 or higher). There were no differences between moon phases in daily admission rates among men, women, young and old patients for any of the stroke subtypes. There was no difference in in-hospital mortality with regard to moon phase for IS or ICH overall (p = 0.19 or higher), nor in subgroup analyses. There were no significant interactions between moon phase and astronomical season for stroke occurrence or in-hospital mortality. To conclude, in this over a decade-long nationwide study including a total of 46 million person years of follow-up, we found no association between moon phases and occurrence or in-hospital mortality rates of IS or intracerebral hemorrhage.     

The progression of 1,2-dimethylhydrazine-induced colon tumourigenesis stimulates growth and cell proliferation in the colon of the host mouse

Abstract. The aim of this study was to characterize tissue responses attributable to the stage of tumourigenesis in CF-1 mice. The study involved initiating colon carcinogenesis by eight weekly subcutaneous injections of 1,2-dimethylhydrazine (DMH at 12mg/kg body weight), while the control mice received injections of the carrier vehicle. All mice were killed for examination of tissue responses at 24 weeks after the completion of the injections. Each mouse was classified into one of four groups based on the histology of the most advanced colonic lesion. The four groups or stages were: 1 no lesions (non-DMH-treated mice); 2 mice with aberrant crypt foci (ACF); 3 mice with one or more adenomas (AD) and 4 mice with an adenocarcinoma (AC). Significant tissue specific responses were identified and related to the stage of tumourigenesis. For example, mice with AC demonstrated a stage specific and marked hypertrophy of the entire colon and spleen, while demonstrating loss of body weight with no change in weight of the thymus or liver. The colonic crypts from these AC-bearing mice demonstrated hyperproliferation and an upward shift of the proliferative zone, with a concurrent loss of iron, but not of calcium, copper, magnesium or zinc in the liver. Splenomegaly was attributed to transition of the tumour to an invasive state. It is proposed that the AC produces a blood-borne trophic factor which helps explain a field effect on the colonic epithelium far removed from the growing AC. This field effect can help explain how biopsy of the large bowel (usually taken from the rectum in humans) can provide morphokinetic information predictive of the stage of colon carcinogenesis.