Mitochondrial function in normal and genetically altered cells and tissues.

Abstract

The impact upon oxidative metabolism of normal and pathological variations of oxidative capability is just beginning to be understood, based upon the few examples of human and animal subject survivals and the relatively few cell systems in which the impact of molecular pathologies on function has been studied. On the one hand, difficulties of isolation of systems containing altered oxidases are significant because of ineffective assembly or small amounts of surviving isoenzymes, and on the other hand, unexpected fragilities of the oxidase system may lead to low yields when subjected to the preparative stresses appropriate to the wild types. To circumvent these problems, this paper describes the application, in vivo, of noninvasive, nondestructive techniques to study the function of cytochrome oxidase and other components of the respiratory chain, particularly cytochromes b-c1 in human subjects on the one hand, and in isolated cells on the other, principally mutants of Saccharomyces cerevisiae in which the subunit content is varied. Two principal spectroscopic approaches are employed: optical and phosphorus magnetic resonance spectroscopy (P MRS). Optical spectroscopy of the near red region of the spectrum provides effective analysis of brain and muscle, as does the surface coil of space-resolved phosphorus magnetic resonance. Both techniques are applicable to suspensions of single cells such as yeast. The optical method yields essential information on oxygen delivery to tissues by hemoglobin and myoglobin and oxygen utilization by cytochrome oxidase. P MRS affords essential information on the efficiency of ATP generation and the extent to which oxidative metabolism meets the needs of cell function in terms of the ratio of phosphocreatine to inorganic phosphate (PCr/Pi). This in turn enables the calculation of the velocity of oxidative metabolism, V, in relation to its maximum capability, Vm, according to a Michaelis-Menten relationship that involves control not only by ADP (Pi/PCr) and Pi, but also by oxygen and substrate deliveries. Thus, an overview of the functionality of mitochondria in cells and tissues is uniquely provided by this combined approach and thereby deficiencies of components of the respiratory chain are quantified.