PHYSIOLOGICAL AND BIOCHEMICAL TECHNICS 187 



A fiirther check of analytical accuracy is the 0/R balance. The O/R 

 balance, or redox index, is the ratio of the number of equivalents of oxida- 

 tion and reduction occurring during dissimilation. Since in any chemical 

 reaction these must be equal, the O/R ratio should be 1. Oxidation- 

 reduction balances are calculated by multiplying the millimoles of 

 product by a value expressing its degree of oxidation or reduction com- 

 pared with the general carbohydrate formula CH2O. The values are 

 positive if the compound is more highly oxidized than CH2O and negative 

 if more reduced. Compared with one oxygen atom with a value of -f-l, 

 two hydrogen atoms have a value of —1. Thus, CO2 has an oxidation 

 value of +2; pyruvic (C3H4O3) and formic (CH2O2) acids, +1; glucose 

 (C6H12O6) and lactic acid (CsHeOs), 0; ethanol (C2H6O) and acetyl- 

 methylcarbinol (C4H8O2), —2 (also known as reduction value if negative) ; 

 etc. It is obvious that the addition or removal of water during the 

 fermentation will not affect the O/R balance, since the O/R value of 

 water is 0. However, the introduction of oxygen into the system w^il] 

 alter the O/R balance, because of the positive O/R value involved. The 

 balance presented above indicates an O/R index of 1.00, which is in 

 excellent agreement with the remaining analytical data. 



The methods of calculation discussed above also may be applied to 

 oxidations involving oxygen or to intermolecular fermentations (e.g., 

 amino acid fermentation such as the Stickland reaction), always provid- 

 ing that the quantities of the participating substrates and products are 

 known. 



The theoretical calculations presented above are based on the assump- 

 tion that the dissimilatory mechanism is kno^vn. The existing knowledge 

 concerning the pathways of microbial dissimilation is, indeed, limited, 

 although data are rapidly accumulating (Elsden, 1952; Gunsalus et at., 

 1955). However, since the results of analyses are often employed to 

 postulate the probable dissimilatory pathway, caution must be exercised 

 in such interpretation. 



More mechanistic studies of substrate dissimilation may be made. 

 Individual stepwise enzymatic reactions may be observed, using dried 

 cells, cell-free enzyme extracts, or purified enzyme preparations. Such 

 reactions involve the breakdown of a given substrate, usually a phos- 

 phorylated compound, to specific end products and may be examined by 

 a variety of technics (Lardy, 1949; Sumner and Somers, 1947; Sumner 

 and Myrback, 1950-1952). Such studies represent some of the final 

 steps in the description of the mechanism of substrate dissimilation; 

 recent advances are discussed contemporaneously in the annual review 

 series for biochemistry and for microbiology (published by Annual 

 Reviews, Inc., Stanford, California). 



