Oscillatory oxidations of reduced pyridine nucleotide by peroxidase

The oscillating peroxidase-oxidase reaction in an open system. Analysis of the reaction mechanism

1. The oscillations in the peroxidase-oxidase reaction in an open system with NADH as the hydrogen donor are caused by the reaction starting and stopping at critical concentrations of the substrates O2 and NADH. The existence of such critical concentrations is typical of branched chain reactions. 2. The critical concentrations of O2 and NADH that determine the initiation of the reaction are mutually dependent. 3. The branching reactions that determine these critical concentrations involve compounds I and II. 4. Superoxide may be involved in the branching reactions by reacting with NADH and ferriperoxidase. At pH 5.1 the rate constant for the latter reaction is determined as 1.5 . 10(5) M-1 . s-1, whereas for the former reaction only an upper limit for the rate constant of 3.5 . 10(4) M-1 . s-1 could be estimated. These relatively low rate constants suggest that alternative branching reactions may also be involved.

Oscillatory kinetics of the peroxidase-oxidase reaction in an open system. Experimental and theoretical studies

1. The oscillations in the peroxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7)-catalyzed reaction between NADH and O2 are undamped when the reaction is carried out in a system open to both substrates and when 2,4-dichlorophenol and methylene blue are present in the solution. 2. The waveform of the oscillations changes when the concentration of peroxidase is varied. 3. The waveforms obtained experimentally can be simulated by a branched chain reaction model in which the branching is quadratic. 4. A correlation between the present knowledge of the reaction and the model can be made by combining well established and hypothetical reaction steps into a few reaction schemes. A selection among schemes however, is not possible at the present time. 5. Compound III participates in the reaction as an active intermediate. This is possible because dichlorophenol stimulates the break down of compound III.

Studies on survival of bacteria: rhythmic response of microorganisms to freeze-drying additives

Various materials were mixed with suspensions of Serratia marcescens and other organisms. Samples were removed and frozen at intervals after mixing; the number of cells that survived both freeze-drying and exposure to air varied rhythmically as a function of time between mixing and freezing. When assayed before or immediately after drying there were essentially no fluctuations. The response was evident only when these dried samples were exposed to air. In a typical experiment, the number of cells surviving in the sample frozen 30 sec after adding propyl gallate was at least 10 times that in samples frozen either 20 sec earlier or 20 sec later. Other "peaks" in survival were observed at approximately 125 and 450 sec, but the times at which the peaks were observed were not consistent from one experiment to the next. Although we have been unable to control or predict the time at which maxima in resistance occur, we have shown that the phenomenon does occur with Escherichia coli and Saccharomyces cerevisiae as well as with S. marcescens. Furthermore, a rhythmic response also was obtained after a change in pH or cell concentration. It appears that microorganisms respond physiologically and synchronously to changes in their environment, and some of these responses have survival value.