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HANDBOOK OF PHYSIOLOGY — NEUROPHYSIOLOGY III 



PHOSPHATE - HIBOSE - GUANINE 



PHOSPHATE - RIBOSE - CYTOSINE 



PHOSPHATE - RIBOSE - URACIL 



PHOSPHATE - RIBOSE - ADENINE 



fig. 5. Schematic representation of a nucleic acid radical. 

 The individual nucleotides are joined by pentose to phosphate 

 bonds at the 2' or 3' position on the pentose chain (points A 

 and B, respectively, of fig. 4, bottom). In brain RNA the relative 

 ratios of purines and pyrimidines are A = 1.00; G = 1.47; 

 C = I.20; U = 0.95 (47). For discussion see text 1971. 



ribosc (or deoxyribose) phosphate groups 'external' 

 to them form the bannisters. 



The nucleotides of figure 4 also have other functions 

 in the cell. By addition of further phosphate groups 

 at position X, di- and triphosphonucleotides are 

 formed. Adenosine triphosphate (ATP) is a familiar 

 example derived from adenine, but other purine and 

 pyrimidine liases are proving to have important roles 

 in cellular economy. Uridine polyphosphates (UDP, 

 LTP) are necessary to galactose metabolism (37, 

 114, lit), 120, 151); cytidine polyphosphates (CDP, 

 CTP) are essential for phosphatide synthesis (122, 

 196); and guanosine polyphosphates (GDP, GTP) 

 are required for protein synthesis (121) and Kiel is' 

 cycle activity at the a-kctoglutarate-succinate stage 

 (199). In addition analogous compounds, di- and 

 triphosphopyridine nucleotides (DPN and TPN, 

 formed from nicotinamide and adenine) and llavine 

 nucleotides (from riboflavin) are important co- 

 enzymes in many steps of energy metabolism. The 

 importance of ATP, DPN, TPN and flavines has 

 been well recognized, bul recent studies by Geiger & 

 Yamasaki (84) indicate thai the others are equally 

 essential, particularly for the maintenance of structure. 



III. Ii 11 « in- !!■_"■< -1 - lli.it nucleic acids, w hicli 



incorporate most of these nucleotides, might function 

 in the cell, together with cn/yme-protein moieties, 

 to carry out reactions demonstrated in ntm with the 

 isolated nucleotides. The nucleotides, nucleic acids 

 and nucleoprotein must, therefore, be considered 

 among the more important unils of structure, organi- 

 zation and function within the cell (28). The studies 



on vims nucleic acid-protein relationships by Fraen- 



kcl-< "Hi 11 I '..0 illustrate this point niceK. A more 



fig. 6. Structural formulae of the posterior pituitary hor- 

 mones. The basic formula shown is the same for all hormone 

 varieties, the only differences being in the amino acids sub- 

 stituted at points X and Y to give oxytocin (0) or vasopressin 

 (P ) of either the lysine or arginine type ( 18, 49, 50). 



general consideration of these subjects has recently 

 been published by Anfinsen (11). 



The structures of proteins synthesized by the 

 mechanisms indicated are in general unknown. 

 However, by modern methods of isolation and 

 analysis some of the simpler molecules or units have 

 been identified. Two examples will indicate the sort 

 of structure or organization to be expected. 



As a result of the brilliant work of du Vigneaud 

 and his collaborators both determination of the 

 structures and synthesis of the posterior pituitary 

 hormones have been accomplished (18, 49, 50). It is 

 now established that these hormones arc elaborated 

 in the supraoptic and paraventricular nuclei of the 

 hypothalamus and arc secreted by these neurons 

 down their axons into the posterior pituitary (105, 

 2IKII. It is probable that the hormones travel with 

 carrier protein (as suggested by AJbers & Brightman 

 (8) as well as the renin-angiotensin system (35) in 

 plasm. 1 1, bin the active principles arc represented bv 

 the structures in figure <>. These are nonapeptides, 

 incorporating nine amino acids by means of peptide 

 bonds ( CH Ml CO CH I. These molecules 

 are not proteins but represent a unit or radical which 

 multiplied ten to thousands of limes would constitute 

 a protein. 



One nl the smaller of such protein molecules is 

 cytochrome c, located mainly in mitochondrial 

 cristae of cells (108, 169) and concerned with the end 

 stage in glucose oxidation, the combination ol 

 hydrogen, derived from various dehydrogenase 

 systems of glucose degradation, with molecular 

 oxygen to form water. Thcorell and his collaborators 



