Hexameric purine nucleoside phosphorylase II from Escherichia coli K-12. Physico-chemical and catalytic properties and stabilization with substrates

Some properties of hexameric purine nucleoside phosphorylase II (EC 2.4.2.1) from Escherichia coli K-12 were studied. The enzyme obeys the Michaelis-Menten kinetics with respect to purine substrates (Km for inosine, deoxyinosine and hypoxanthine are equal to 492, 106 and 26.6 microM, respectively) and exhibits negative kinetic cooperativity towards phosphate and ribose-1-phosphate. The Hill coefficient is equal to approximately 0.5 for both substrates. Hexameric purine nucleoside phosphorylase II is not a metal-dependent enzyme; its activity is inhibited by Cu2+, Zn2+, Ni2+ and SO4(2-). The enzyme is the most stable at pH 6.0; it contains essential thiol groups. All substrates partly protect the enzyme against inactivation by 5.5'-dithiobis(2-nitrobenzoic acid) and heat-inactivation and, with the exception of phosphate-against inactivation by p-chloromercuribenzoate. Hypoxanthine, especially in combination with phosphate, afford the best protection against inactivation.     

Die Wuchsstoffleitung in der Pflanze I

Zusammenfassung In Blättern vonColeus-rot und in Kotyledonen vonCucumis sativa wird künstlich durch die Epidermis zugeführter Wuchsstoff (Heteroauxin) apikalwärts geleitet, wenn der direkte Abfluß nach der Mittelrippe unterbunden ist. Daraus folgt, daß die Wuchsstoffleitung in der Pflanze keine streng polare Erscheinung ist, genau so wenig, wie der Transpirationsstrom oder der Strom der Assimilate streng polar fließen.Mit 11 Textabbildungen (16 Einzelbildern).Mit Unterstützung der Deutschen Forschungsgemeinschaft und der William G. Kerckhoff-Stiftung zu Bad Nauheim.     

An improved glucoseoxidase--peroxidase-coupled assay for -fructofuranosidase activity

An improved glucoseoxidase-peroxidase-coupled assay for the determination of β-fructofuranosidase activity is described. The method makes use of the double effect of Tris (2-amino-2-hydroxymethylpropane-1,3-diol) as an inhibitor of both invertase and contaminating glucosidases. The method is very sensitive and is suitable for routine determinations. The total time needed for a single analysis is less than half an hour.     

Mathematical model of autoimmunity]

A mathematical model of autoimmunity is developed. This model is a system of two nonlinear differential equations, which describe the concentration dynamics of tissue cells and agressive lymphocytes. An analysis of the solutions shows that this model reproduces general behaviour of autoimmune diseases.     

Role of the adrenal cortex and sodium in the pathogenesis of human hypertension.

After 30 years of continuous research into the mechanisms of human hypertension, we summarize the results obtained by the members of the multidisciplinary research group on hypertension of the Clinical Research Institute of Montreal on the disturbances of minerlocorticoid activity in a rigorously selected group of patients with early, mild essential hypertension. We attempt to integrate these findings with those of many other groups working on other aspects of hypertensive cardiovascular diseases. On the assumption that the increased peripheral resistance responsible for hypertension results from an imbalance or a disturbance of the equilibrium between the sympathetic nervous system and norepinephrine on one hand, and the vascular tone, sensitivity and responsiveness of the arterial smooth muscle to norepinephrine and to angiotensin II on the other hand, three models that fit the experimental and clinical facts as known at present are described.