METABOLIC PRODUCTS 281 



fresh medium with a high glucose content but low in other nutrients 

 (Forges et al, 1940, 1941). 



The production of gluconic acid appears to be a direct oxidation of 

 glucose. The enzyme responsible for this transformation is called glucose 

 aerodehydrogenase. This enzyme, when free from catalase, catalyzes a 

 reaction between glucose and oxygen. Gluconic acid and hydrogen 

 peroxide are the products formed. Glucose aerodehydrogenase was first 

 isolated from Penicillium chrysogenum and was called notatin, or penicil- 

 lin B, at first. Its antibiotic activity is due to liberation of hydrogen 

 peroxide. For recent papers on this enzyme see Keilin and Hartree 

 (1948, 1948a). 



Lactic acid. Various lactic acid bacteria are used in the commercial 

 production of lactic acid. These bacteria require a complex natural 

 medium, which makes the purification of lactic acid laborious. Many 

 species of Phycomycetes produce lactic acid, and species of Rhizopus are 

 noteworthy in this respect. The following fungi produce lactic acid: 

 Rhizopus arrhizus, R. chinensis, R. elegans, R. japonicus, R. nodosus, R. 

 oryzae, R. pseudodiinensis, R. salehrosus, R. shanghaiensis, R. stolonifer, 

 R. tritici, Mucor rouxii, Monilia tamari, and Blastocladia pringsheimii. 

 Most of these fungi appear to synthesize c?-lactic acid, although R. 

 chinensis synthesizes Wactic acid (Saito, 1911). 



The use of R. oryzae for production of lactic acid has been intensively 

 investigated (Lockwood et al., 1936; Ward et at., 1936, 1938). Glucose 

 appears to be the best sugar. Nitrate nitrogen is not used by this fungus. 

 Calcium carbonate is used in the medium to neutralize lactic acid as it is 

 formed. Yields increase when the cultures are aerated. As much as 

 75 per cent of the glucose utilized is converted into lactic acid. The 

 presence of added zinc increases mycelial growth but depresses the yield 

 of lactic acid. 



The mechanism of lactic acid production by fungi is ably discussed by 

 Foster (1949). Under anaerobic conditions, ethyl alcohol, carbon 

 dioxide, and lactic acid are produced in equimolecular amounts. The 

 amount of lactic acid produced under aerobic conditions increases, while 

 the amount of alcohol decreases (Waksman and Foster, 1939). The 

 most probable intermediate for the production of lactic acid is pyruvic 

 acid. 



Itaconic acid. Aspergillus itaconicus was the first fungus reported to 

 synthesize itaconic acid. The structural formula below shows that this 

 unsaturated acid is related to succinic acid. 



CH2=C— COOH 



HoC— COOH 

 Itaconic acid 



