| Comments |
P.303 left column 3rd paragraph: "At a first glance, it may appear paradoxical that tumor cells with high rates of glucose-consumption and lactate production possess a pyruvate kinase isoenzyme which is inactive. However, the inactive dimeric form of M2-PK which is not associated within the glycolytic enzyme complex has the metabolic advantage that the phosphometabolites above pyruvate kinase, such as PEP, glycerate 3-P, glyceraldehyde 3-P, fructose 1,6-P2, ribose-5P and 5-ribose-PP accumulate and are then available as precursors for synthetic processes, such as nucleic acid, amino acid and phospholipid synthesis which all branch off glycolysis (Fig. 1, Table 1) [refs 5,12,15,22,23,26]. The mass of ribose 5-P is synthesized by the transketolase/transaldolase reaction due to an inhibition of the oxidative pentose-P cycle by high fructose 1,6-P2 levels [ref 39]. In tumor cells, phosphometabolite levels are about 100-fold higher than in differentiated cells." |