論文

OCl-/HOCl imposed a rapid inactivation of catalase (hydrogen-peroxide: hydrogen-peroxide oxidoreductase, EC 1.11.1.6), some of which was slowly reversible upon subsequent exposure to H2O2. Ethanol accelerated this restoration of activity by H2O2. OCl- caused biphasic changes in the visible absorption spectrum of catalase, which were partially reversed by dithionite. A scheme of reactions involving axial ligation of one or two OCl- to heme iron, followed by heterolytic or homolytic cleavages of the OCl bond, is proposed to account for the behavior of the system. © 1988.

Cyanide catalyzes the reduction of dioxygen or of ferricytochrome c by dihydroxyacetone phosphate. The rapid initial phase of these reactions, but not the subsequent slow phase, was augmented by incubating the triose phosphate aerobically or anaerobically at pH 9.0 prior to adding the cyanide. The aerobic incubation, which was most effective, was associated with a decline in enediol, whereas the less effective anaerobic incubation was accompanied by an increase in enediol content. This suggested that the α-ketoaldehyde product of autoxidation of the enediol, rather than the enediol itself, was responsible for the rapid phase reaction which followed addition of cyanide. This was confirmed by exploring the cyanide-catalyzed oxidation of the α-ketoaldehyde, phenylglyoxal. The inhibitory effect of the manganese-containing superoxide dismutase indicated that O2- was a kinetically important intermediate of the rapid phase reaction. A reaction mechanism is proposed which is consistent with the results presented. © 1987.

Increasing the intracellular flux of O2- by incubating aerobic Escherichia coli with paraquat or plumbagin markedly lowered the α,β-dihydroxyisovalerate dehydratase activity detectable in extracts from these cells. This effect was not seen in the absence of dioxygen and was exacerbated by inhibiting protein biosynthesis with chloramphenicol. These effects of paraquat and of plumbagin were both time- and concentration-dependent. Transfer of E. coli from aerobic to anaerobic conditions caused a rebound of the dehydratase activity, in the continued presence of paraquat and of chloramphenicol, indicating the presence of a mechanism for reactivating this enzyme. The instability of the dehydratase activity in cell extracts was exacerbated by selective removal of superoxide dismutase, but not of catalase, by immunoprecipitation. Addition of exogenous superoxide dismutase reversed the effect of immunoprecipitation; whereas catalase or inactive superoxide dismutase were ineffective. We conclude that the dehydratase is inactivated by O2-. This could account for the bacteriostatic effects of dioxygen and of paraquat.

The interactions of urea, trimethylamine-N-oxide (TMAO), and related solutes on a number of enzymes were examined. Urea inhibited enzymatic activity and accelerated the thermal inactivation of catalase, whereas TMAO activated some enzymes but inhibited others. The effects of urea and of TMAO, whether parallel or in opposition, were exerted independently. Thus, in those cases where TMAO increases enzymatic activity, it did so to the same relative degree, whether or not urea was present. TMAO markedly decreased the rate of thermal inactivation of catalase, indicating that it does favor compact protein structures. The assumption that TMAO factors compaction of protein structure, whereas urea has the contrary effect, does not lead to the expectation that TMAO must always oppose the effect of urea on enzymatic activity, since the most compact form of an enzyme may not always be the most active form. © 1987.

The aerobic xanthine oxidase reaction causes the cooxidation of dihydroxyacetone in a process which is strongly inhibited by superoxide dismutase but not by catalase, HO · scavengers, or iron-inactivating chelating agents. Several molecules of the sugar can be oxidized per O2- introduced. A free radical chain mechanism, in which O2- acts both as an initiator and as a chain propagator, is proposed. Simple sugars capable of tautomerizing to enediols may now be added to the list of biologically relevant targets for O2-. © 1987.

The reaction of nucleotides with superoxide gave the corresponding nucleobases in good yield. The base-release reaction of nucleotides due to superoxide was examined and compared to that of nucleosides. Hence, the phosphate moiety greatly enhances the yields, in particular those of adenine from adenosine monophosphates. Superoxide in combination with the phosphate moiety has been revealed to be more active than superoxide alone. The phosphate peroxy radical, generated in situ from superoxide and phosphate, seems to be the species responsible for the formation of the free bases. © 1987.

The clusters [Fe4S4(SR)4]n- (n=3) generated electrochemically reduced imines to amines in a CH3CN/CH3OH solution. The correlations between the redox potentials of imines and the yields of the reductions were examined. © 1983.