METABOLIC FUNCTIONS OF B VITAMINS 235 



extent the enzyme systems capable of the conversion of the single carbon 

 unit to utilizable methyl groups is indicated in an abstract reporting the 

 choline-sparing action of vitamin Bi 2 in the nutrition of rats and chicks. 44 

 Porphyrins. Lack of either folic acid 45 or vitamin B12 4C (in rats) 

 results in a decrease in porphyrin synthesis, indicating a possible role of 

 the single carbon unit in porphyrin metabolism. A recent report indicates 

 that glycine may be a complete substitute for the folic acid requirement 

 needed for normal porphyrin synthesis. 45 Thus the involvement of the 

 catalysts of the single carbon unit may be partially or wholly due to their 

 role in the production of glycine from serine. Glycine had previously been 

 shown to be one of the metabolic units needed for the biosynthesis of the 

 pyrrol rings in the porphyrin nucleus. 47 Isotopically labelled acetate has 

 also been shown to be incorporated into the porphyrin structures, impli- 

 cating a pantothenic acid requirement for porphyrin synthesis. 48 



Fundamental Physiological Processes Requiring Energy 



Knowledge concerning the mechanisms by which the chemical energy 

 inherent in the organic substrates metabolized by organisms is converted 

 into other forms of energy must serve as the basis for understanding the 

 fundamentals of physiological processes. By the degradation of organic 

 substrates, and in some cases oxidation of inorganic substances, living 

 organisms transform chemical energy into mechanical energy (including 

 work against osmotic pressure), thermal energy, electrical energy and 

 radiant energy. What is known concerning the role that the B vitamins 

 play in these energy transformations? 



Chemical Energy. The general mechanisms by which the energy re- 

 leased during the oxidation or degradation of organic compounds is made 

 available to organisms for other purposes which require an energy supply 

 has been previously indicated. In almost all cases it appears that the 

 energy is conserved, transported, and eventually utilized through the in- 

 termediate formation of compounds that are acid anhydrides of phos- 

 phoric acid, compounds containing the so-called "high energy phosphate 

 bonds." 49 - 50 



Three types of reactions for which there is some evidence indicating 

 the mode of formation of the energy-carrying phosphate bonds have been 

 discussed in connection with the reactions catalyzed by the coenzymes of 

 nicotinic acid, thiamine, and pantothenic acid: 



(1) The dehydrogenation of an aldehyde-inorganic phosphate addition 

 product by the coenzymes of nicotinic acid in effect utilizes the energy 

 derived from the oxidation of an aldehyde to an acid to convert a 

 molecule of inorganic phosphate to an energy-rich acyl phosphate. (See 

 p. 140 for the mechanism.) 



