236 THE BIOCHEMISTRY OF B VITAMINS 



(2) The energy liberated in the coupled dehydrogenation and decar- 

 boxylation of the inorganic phosphate — carbonyl addition products of 

 pyruvic acid and ot-ketoglutaric acid by thiamine-containing enzymes 

 produces the energy-rich phosphorylated intermediate (p. 163 and 167). 



(3) The degradation of the inorganic phosphate — carbonyl addition 

 product of /?-ketoacyl phosphates (for example, acetoacetyl phosphate) 

 results in the cleavage of a carbon-to-carbon bond and the formation of 

 an additional acyl phosphate (p. 189) . 



In addition to these reactions it has been shown that in aerobic proc- 

 esses additional inorganic phosphate is converted into energy-laden pyro- 

 phosphates by the reactions in which the hydrogen atoms are transported 

 to oxygen via the riboflavin and porphyrin-containing enzymes. 49 In these 

 instances the mechanism by which the phosphate transformation is 

 coupled to the transfer of hydrogen atoms is unknown, but it has been 

 postulated to take place through the addition of phosphoric acid to 

 ethylenic bonds. 49 



Conversely, the energy of the phosphate bonds may be utilized for 

 synthetic purposes by serving as the sources of energy for the formation 

 of glucosidic, ester, and probably peptide bonds (reactions requiring no 

 B vitamins) and for the reductions and condensations catalyzed by nico- 

 tinic acid, thiamine, and pantothenic acid (reactions which are the reverse 

 of those tabulated for the formation of the energy-laden bond) . 



Mechanical and Thermal Energy. On the basis of the current state 

 of knowledge it appears that the B vitamins, having catalyzed the proc- 

 esses by which the high-energy phosphate bonds are formed, have no 

 further function in transforming this energy into either mechanical work 

 or thermal energy. Thus, in none of the following instances has a B vita- 

 min requirement been shown: the contractions of muscle are the result 

 of the transformation into kinetic energy of the energy liberated during 

 the hydrolysis of adenosine triphosphate by an enzyme, adenosine triphos- 

 phatase (a component of muscle myosin) 50 ; the chemical mechanisms 

 involved in protoplasmic movement (which are responsible for the con- 

 tractility and mobility of living cells) are not yet understood; the work 

 against osmotic pressure, performed during absorption, is a process often 

 involving phosphorylation of the absorbed molecules by adenosine tri- 

 phosphate; extra thermal energy (over and above that normally resulting 

 from metabolic processes) can be produced by the hydrolytic action of 

 pyrophosphatases 23 upon the energy-rich bonds, causing the dissipation 

 in heat of all the energy of the bonds. 



Electrical Energy. Little can be said concerning the manner in which 

 the energy derived from metabolic reactions is utilized to establish the 

 electrostatic membrane potentials maintained by viable cells or concern- 



