CARL F. CORI 



understanding will have far-reaching consequences for biology 

 as a whole and that it will be of great benefit in the treatment of 

 disease. In a sense the problem has been worked on extensively 

 in the past on a variety of unicellular organisms. There is also 

 available a large amount of information which is based on work 

 on the intact animal, with a variety of methods, including more 

 recently the use of isotopes. The study of regulatory mech- 

 anisms and the endocrine control of metabolism fall into this 

 category. 



In this article an attempt will be made to outline some of 

 the problems which arise in this field, and to point out certain 

 areas where additional information is needed. It is not in- 

 tended to cope with a vast, quite heterogeneous, and widely 

 scattered literature or to treat any given problem exhaustively. 

 The field will be narrowed down further by considering mainly 

 mammalian cells. 



Rate of Penetration of Sugars into Cells 



One of the first questions which arises is that of rate of 

 penetration of various substances through the cell membrane. 

 For example, is it the rate of entrance of metabolites, more or 

 less common to all cells, such as sugars, amino acids, fatty acids 

 and their keto derivatives, which determines the rate of metab- 

 olism within the cell, or are the rate-limiting steps the enzy- 

 matic reactions in which these metabolites are used as sub- 

 strates? In the first case the cell membrane would have a con- 

 trolling influence over the rate of metabolism ; in the second case 

 the effective enzyme concentration would be decisive. In 

 spite of a very large literature on the subject of permeability, 

 information on this question is very scanty. 



Work carried out recently in this laboratory by Drs. Field, 

 Heimberg, and Crane and not as yet reported has given a defi- 

 nite answer to this question for the Ehrlich ascites tumor cells 

 metabolizing various sugars. These washed, single-cell prep- 

 arations show one of the highest rates of glucose catabolism 



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