Mitochondrial Structure and Fuuctiou 



DAVID E. GREEN 



University of Wisconsin 

 Madison, Wisconsin 



THE MITOCHONDRION IS A BIOCHEMICAL MACHINE, Universally distributed in all 

 aerobic organisms, which oxidizes pyruvic acid to carbon dioxide and water 

 by way of the citric acid cycle and which links these oxidative reactions involving 

 molecular oxygen to synthesis of adenosinetriphosphate (ATP). In some mito- 

 chondria, oxidative reactions other than those of the citric acid cycle may be 

 coupled to synthesis of ATP, but there appears to be no known exception to the 

 rule that all mitochondria carry out the citric acid cycle. Most mitochondria carry 

 out reactions other than those of the citric acid cycle and other than oxidative re- 

 actions, but we shall not be concerned with these processes in the context of the 

 present talk. 



We may define some of the basic biochemical problems of the mitochondrion 

 in terms of the following broad questions: 



/) How are the enzymes arranged .-^ Are they organized in a definite pattern.'' 



2) What is the physical state of the mitochondrion.'' Can we think of the mito- 

 chondrion as a particle in which all the component parts are rigidly positioned 

 with respect to one another and held together in chemical bonding, or are the 

 components in solution within the mitochondrial interior and interacting with one 

 another by thermal collision.'' 



^) How are the enzymes which implement the citric cycle geared to the elec- 

 tron transport chain, and how in turn is electron flow coupled to oxidative phos- 

 phorylation.'' 



As you may be aware, our laboratory has been intimately concerned with these 

 problems during the past 12 years, and I would like to summarize for you in 

 capsular form some of our experimental observations and present working 

 hypotheses which bear on the problems I have just defined. 



One of the greatest impediments to the biochemical study of the mitochondrion 

 has been the functional instability of isolated mitochondria. Liver suspensions, for 

 example, have a half-life time of several hours at best. About 5 years ago we ex- 

 plored the possibilities of heart mitochondria as a stable source of material for 

 large scale isolation, and this material turned out to be just what the doctor 

 ordered. They can easily be prepared from slaughterhouse material on any de- 

 sired scale; they are incredibly stable even to freezing and thawing (19); they are 

 readily fragmented into stable particles; and they have made it possible for our 



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