VI INTERMEDIARY METABOLISM AND GROWTH I23 



VI. ADDENDUM 



j) The lipid cofactor can be replaced by a group of 2,3-dimethoxy-5-methyl- 

 benzoquinone compounds which are substituted at position 6 with homologous 

 isoprenoid chains. The latter compounds (Coenzymes Qg to Q,jq) have been 

 isolated from lipides of beef heart mitochondria and microbial sources and 

 undergo cyclic oxidation and reduction during substrate oxidation (R. L. Lester, 

 F. L. Crane and Y. Hatefi, (1958), J. Am. Chem. Soc, 80, 4751). 



2) A soluble RNA residing in the same cellular fraction which activates amino 

 acids reversibly binds amino acids in the presence of ATP. Since the amino acid 

 so bound can be subsequently transferred to microsomal protein in the presence 

 of GTP, the RNA-amino acid may be an intermediate in microsomal protein 

 synthesis (M. B. Hoagland, M. L. Stephenson, J. F. Scott, L. I. Hecht and 

 P. C. Zamecnik, (1958), J. Biol. Chem., 2ji, 241). 



3) Recent evidence indicates that isocitric lysase and the malate condensing 

 enzyme function in a "glyoxylate cycle", thereby providing a route for the net 

 conversion of fat to carbohydrate by plants (H. L. Kornberg and H. Beevers, 

 (1957), Biochim. et Biophys. Acta, 26, 531): 



glyoxylate 



a) Fat -^ acetyl-CoA > malate -^ carbohydrate 



b) 2 Isocitrate -^ a-ketoglutarate + glyoxylate + succinate + COj 



c) a-Ketoglutarate + succinate -^ 2 oxalacetate + CO2 



d) 2 Oxalacetate + 2 acetyl-CoA — » 2 isocitrate 



4) Glutamine functions as an amino donor in the conversion of uridine nucleo- 

 tides to cytidine nucleotides by rat tumor enzymes (H. O. Kammen and R. B. 

 Hurlbert, (1958) Biochim. et Biophys. Acta, 30, 196). Glutamine-^^N is also a 

 precursor of asparagine-^^N in human cells in tissue culture (L. Levintow, 

 (1957) Science, 126, 611). 



5) Recent evidence suggests that mevalonic acid (dl-[3, y-dihydroxy-[i-methyl- 

 valeric acid), 5-phosphomevalonic acid, 5-pyrophosphomevalonic acid, and 

 A^-isopentenol pyrophosphate are intermediates in squalene synthesis. New 

 carbon-carbon bonds between two isoprenoid units are formed by the interaction 

 of two methylene groups while the carboxyl groups of mevalonic acid are lost 

 in a concerted process with simultaneous elimination of the tertiary hydroxyl 

 groups, and the formation of a double bond between Cj and C, (S. Chaykin, 

 J. Law, a. H. Phillips, T. T. Tchen and K. Bloch, (1958) Proc. Natl. Acad. 

 Sci., U.S., 44, 998. 



Carbon 28 of yeast ergosterol is formed by the transmethylation of the methio- 

 nine methyl group to C24 of an intermediate beyond squalene. In experiments 

 with '"^CHj-methionine, it was shown that ergosterol but not zymosterol nor 

 lanosterol were labelled (G.J.Alexander, A. M. Gold and E. Schwenk, (1958) 

 J. Biol. Chem., 232, 599). 



Literature p. 124 



