722 DYNAMIC ASPECTS — AMINO ACID POOL TURNOVER 
IN VIVO COMPARTMENTS OF GLUTAMIC ACID METABOLISM 
IN BRAIN AND LIVER* 
HEINRICH WAELSCH 
New York Psychiatric Institute and Columbia University, College of Physicians and Surgeons, 
New York, N.Y. (U.S.A.) 
For the biochemist primarily engaged in the study of brain metabolism the relation- 
ship between structure and intermediary metabolism of this organ is a problem of 
immediate urgency. The brain’s structure, the most complex of any organ of the 
mammalian body, must be correlated with its metabolism in order to understand 
and evaluate the metabolism, as such and its implications for cerebral function. 
It has been suggested that the concept of metabolic compartments or metabolic 
pools satisfies a unifying concept of structure and metabolism! *. In living matter 
there exist metabolic compartments on all levels of organization: the organ, the 
tissue, the cells and the subcellular units. On each level of organization there are 
compartments of different order of homogeneity characterized by their concentra- 
tion of enzymes and metabolites and separated by structural features such as mem- 
branes, fibers and interstitial components. The compartments are in communication 
with each other: they are not closed to one another, but are in a dynamic relationship. 
Some metabolites are produced in one and used in another, some stored here and 
adsorbed on active sites there, some transported by the blood or interstitial fluid to 
receptor sites, some being part of one transport system and some diffusing from one 
compartment to another. Macromolecules such as enzyme proteins might stay in 
one place, but are dependent in their activity on the concentration of coenzymes and 
on their own rate of rejuvenation. 
Neurophysiologists in particular have used the concept of compartments and 
their interrelationships consciously or unconsciously for many years in their studies 
of the forces responsible for the separation and movements of ions across membranes. 
In an organ such as the nervous system function is essentially a membrane pheno- 
menon; the properties of the membranes are the results of the dynamic interaction 
of the metabolic compartments on either side and the specific structure. 
In examining the central nervous system we become aware of the number of 
metabolic compartments in different levels of organization. A rough survey from the 
microscopic to the subcellular is given in Table I. The significance of metabolic 
compartments for the metabolism of the central nervous system immediately be- 
comes apparent if we consider the cerebral glucose and energy metabolism. Although 
at present the mechanism of transport of glucose into the brain from the blood is 
unknown, its utilization appears to be controlled by the rate of its metabolism rather 
* This presentation is based in part on a lecture given on the occasion of the Sesquicentennial 
Anniversary Symposium at McLean Hospital, Belmont, Massachusetts. Since the author was 
unable to attend, the paper was not presented at this Conference but is included in the Proceedings. 
References p. 730 
