Physiological processes kinetic investigations

The ferriheme protein metmyoglobin (metMb) at the physiological pH 7.4 was reported to bind the NO molecule reversibly yielding the nitrosyl adduct [metMb(NO)] the kinetics of the association and dissociation processes were investigated and a limiting dissociation mechanism was proposed (58,68). 2-His-l-Glu nonheme iron center engineered into myoglobin was reported capable to bind Fe(II) and reduce NO to N2O (69). 

Whenever possible the basic molecular events of physiological processes are studied in detail in solutions either in parallel with, or as a guide to, experiments on the organized system. For example, the study of the reactions of myosin and the associated proteins of the contractile cycle, by the methods used for the investigation of mechanisms of soluble enzymes (see section S.l), has helped in the planning of experiments and in the interpretation of the events observed in muscle fibres. The most useful methods for kinetic studies on physiological functions are those which can be applied to systems at different levels of organization. We shall return to them at the end of this chapter. 

The principles of design and interpretation of kinetic investigations with photolabile precursors can be best illustrated by some of the many uses of npe-ATP. The important parameters to be determined with each compound are the absorption spectrum, quantum yield, rate of appearance of active substrate, the possible binding (competitive inhibition) of the caged compound and the effects of any photoproducts. Additional to these compound specific parameters, instrumentation parameters have to be considered. These are concerned with the light source for photolysis and with the detection equipment. The latter can either monitor the photolytic reaction of the caged compound or the physiological process stimulated by... 

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