Fig. 1

Besides as constituents for protein synthesis, AAs provide carbon and nitrogen sources for the syntheses of nucleobases, and consume a large portion of ATP. a. AAs including asparate, glutamine, serine and glycine provide the essential carbon and nitrogen sources for the syntheses of nucleobases [15]. Those carbons and nitrogens highlighted in various colors represent their original sources, such as asparate (brown), glutamine (blue), serine and folate cycle (purple), glycine (green) and bicarbonate radical (tan). b. The proportions of ATP-consuming processes in thymocytes [3]. AA metabolism may use up to ~ 58% of the total ATP consumption including protein synthesis (~ 33%) and nucleotide synthesis (~ 25%)