222 Discussion 



being on the left-hand side and the products being on the right-hand side. 

 Although it is possible to take into account reversibility of these reactions, 

 this is omitted for the sake of simplicity in this preliminary study. 



The equations in the category labelled "phosphorylation of glucose" 

 represent the combination of glucose (GLU) concentrations between 

 zero and 4 x 10-^ m with 10-^ m hexokinase (ENZ) with a velocity 

 constant of 3 x 10-^ m-^ sec~^ to form a glucose enzyme intermediate 

 (ENG). Any reactant that disappears in the chemical change must be 

 so indicated on the right-hand side and the reaction product is written 

 ENG — GLU — ENZ. The second step is the reaction of the glucose- 

 enzyme intermediate (ENG) of zero initial concentration with 10-^ m 

 ATP available in store I (ITP), with a velocity constant of 6 x 10-* m-i 

 sec-i to form ADP (which is not compartmented) plus the free enzyme 

 (ENZ) plus glucose-6-phosphate (GLP) together with a notation of those 

 substances which are expended in this reaction (— ENG — ITP). The 

 isomerase step is assumed not to be rate-limiting and GLP is reacted 

 directly with phosphohexokinase (ETZ) to form an intermediate which 

 in equation 4 reacts with ATP to form fructose diphosphate (GPP). In 

 the aldolase reaction (equation 5) the enzyme-substrate intermediate 

 is omitted and a first-order velocity constant of 10^ sec.-^ leads to the 

 formation of two molecules of reaction product. The isomerase step is 

 omitted and it is assumed that all of the dihydroxyacetone phosphate 

 can be made available as glyceraldehyde phosphate (GAP). 



In order to reduce the number of equations and to simplify the 

 calculations, enzyme substrate intermediates are omitted in equations 

 6-15 and, instead, a velocity constant for the second order reaction of 

 the two substrates is included. In the glycolytic phosphorylations of 

 ADP (equation 6), glyceraldehyde phosphate (GAP) (at an initial 

 concentration of zero) reacts with 10-* m DPN (DPN) with a velocity 

 constant of 10-^ m-^ sec-^ to give reduced DPN and an intermediate 

 BGA. For simplicity, the separate steps of GAP and DPN with the 

 enzyme are omitted, and BGA represents the enzyme-substrate- 

 coenzyme complex. In equation 7 the phosphorolysis of this complex 

 with 5 X 10-3 ^j inorganic phosphate (PIA) is represented to have a 

 velocity constant of 10'. The reaction product, 1 : 3-diphosphoglyceric 

 acid (DGA) then reacts with ADP with 10-* m ADP at a velocity 

 constant of 10^ to form ATP of store I (ITP) and 3-phosphoglyceric 

 acid (PGA). At this point both the phosphoglyceromutase and enolase 

 steps are assumed not to be rate-limiting steps and the overall reaction 

 from 3-phosphoglyceric acid to pyruvate (PYR) is written as a single 

 step. In equation 9, ATP available to store I is formed (ITP). 



Equations 10 and 11 represent the lactate-pyruvate equilibrium and 

 constitute the pyruvate store. Therefore, appropriate initial concentra- 

 tions of these two substrates are based upon the equilibrium constant. 

 These concentrations together with the initial concentrations of DPNH 

 (DPH) and DPN (DPN) afford a supply of metabolites for the mito- 

 chondria. 



Reactions occurring within the mitochondrial membrane are indicated 

 by equations 12, 13 and 14, and all of the processes of the citric acid 



