Are spontaneous conformational interconversions a molecular basis for long-period oscillations in enzyme activity?

Soluble and immobilized catalase. Effect of pressure and inhibition on kinetics and deactivation

This article examines the effect of pressure on the steady-state kinetics and long-term deactivation of the enzyme catalase supported on porous alumina. The reaction studied is the decomposition of hydrogen peroxide. The results of studies carried out in a continuous stirred-tank reactor under isothermal conditions are presented and compared with results obtained for soluble catalase. For soluble catalase, it is found that in the range of pressures studied, the oxygen flow rate increases with increase in pressure up to a certain value and then decreases. Hydrogen peroxide concentration appears to have a strong influence on pressure effects. With immobilized catalase, the pressure effects are not as prominent. Fluorescent microscopy studies of the immobilized enzyme suggest that this is probably because of pore diffusional limitations.

In vitro slow fluctuation in horseradish peroxidase activity

In vitro slow fluctuations in the level of horseradish peroxidase activity were observed in long-range experiments (72-144 h). Besides random fluctuations, regular slow oscillatory patterns with period lengths ranging from 10.0 to 39.0 h were detected by statistical analysis. The possibility that these oscillations in enzyme activity could have reflected changes in the physical environment of the experimental setup has been thoroughly examined and ruled out. Periodic exposition of the enzyme solution, otherwise kept in darkness, to blue light illumination was shown to influence the period of the oscillations. The changes in enzyme activity were correlated with a modification of the Michaelis constant estimated using guaiacol as substrate. This result was confirmed by the action of chemical modifiers of the enzyme, such as ferulic acid and rutin. It is thought that the observed oscillations in horseradish peroxidase activity are due to spontaneous and specific changes in the tridimensional structure of the enzyme in the thermic reservoir.

Multiple levels in the control of rhythms in enzyme synthesis and activity by circadian clocks: recent trends

It is now well established that circadian clocks can control rhythmicity at different stages of the sequence of events leading from gene activity to a functional enzyme molecule. Conceptual and experimental distinction of the effective control targets is emphasized, with particular attention to recent results obtained on circadian clock control of transcription and to data indicating that proteins can behave as conformational oscillators. Thus circadian rhythmicity both in gene expression and in the dynamics of the enzyme molecule would contribute to the temporal compartmentation of processes such as metabolic co-ordination and channeling necessary for the adaptive efficiency of physiological programmes.