BIOCHEMISTRY OF MICRO-ORGANISMS 



113 



the organism for the specific purpose of 

 converting molecular into combined nitro- 

 gen. The studies of Steinberg (1937), 

 from which it appears that the common 

 mold Aspergillus niger also needs traces of 

 molybdenum, particularly when grown in 

 nitrate media, combined with the studies 

 by Arnon (1938), which show the same 

 needs for higher plants, generally growTi 

 with nitrate nitrogen, all point in the di- 

 rection that for the reduction of nitrogen 

 compounds some molybdenum catalyst is 

 necessary. Observations like these may 

 ultimately lead to the isolation of the 

 catalyst, which, in turn, would materially 

 aid in studying the mechanism of nitrogen 

 fixation. Kuhn (1938) has recently re- 

 ported the formation by micro-organisms 

 of a specific compound, borocitrin, appar- 

 ently closely related to the flavin pigments, 

 and like these capable of undergoing rever- 

 sible oxidation-reductions. The produc- 

 tion of this substance is strictly dependent 

 upon the presence of boron in the culture 

 medium, and the elucidation of its physio- 

 logical function may be expected to throw 

 considerable light on the necessity as well 

 as on the role of boron which has been 

 established as one of the essential elements 

 for plant growth (Hoagland 1937). 



The relations between organic "growth 

 factors," vitamins and enzymes also is 

 obvious in many cases. The recent studies 

 by various investigators have conclusively 

 shown the vitamin nature of the active 

 (prosthetic) groups of a number of the 

 most important enzymes. To make this 

 clear, it may suffice to mention the studies 

 on vitamin Bj (Aneurin) and its pyro- 

 phosphate derivative, which is identical 

 with the prosthetic group of the enzyme 

 carboxylase; those on vitamin B2 and its 

 relation with the "yellow enzymes" of 

 which it is the prosthetic group ; and the 

 studies on the anti-pellagra vitamin which 

 is identical with nicotinic acid amide, the 

 most important part of the prosthetic 

 groups of the dehydrogenases. The rela- 

 tionships in other cases are clearly indi- 

 cated. I need here but refer to vitamin A 

 and the existence of a reversible "enzyme- 



system" of a similar chemical nature in 

 the retina (Wald 1935) ; to the spectacular 

 studies of Moewus et al. (Moewus 1938; 

 Kuhn, Moewus and Jerchel 1938), from 

 which it appears that only one molecule of 

 crocin per cell might induce the activity of 

 flagellae in Chlamydomonas eugametos, 

 and that the methylesters of cis- and trans- 

 crocetin in somewhat larger quantity and in 

 different proportions cause either the male 

 or the female gametes to become capable of 

 conjugation ; and to the recent isolation and 

 identification of vitamin Bg (Harris and 

 Folkers 1939) as a simple pyridine deriva- 

 tive. These illustrations suggest future 

 discoveries of as many more enzyme sys- 

 tems at present unkno^vn. 



In this field the micro-organisms likewise 

 may be of great significance. It is possible 

 now to use them for rapid and inexpensive 

 assaying of vitamins (Snell and Strong 

 1939), and they may serve as material for 

 studying the particular phases of metab- 

 olism in which vitamins, with as yet little- 

 known functions, operate. Lwoff and co- 

 workers, and Knight et al. have published 

 some fine examples of studies of this kind. 



So far this discussion may have shown 

 how experiments with various types of 

 micro-organisms have contributed towards 

 the development of fundamentally impor- 

 tant problems and viewpoints in physi- 

 ology and biochemistry. Although the 

 details of many of these processes have 

 not yet been satisfactorily and completely 

 worked out, the great lines and general 

 principles are clearly evident. 



The preceding review has dealt prima- 

 rily with the breakdown processes in metab- 

 olism. Studies on micro-organisms should 

 also yield much information on synthetic 

 reactions. From the end of the 19tli cen- 

 tury on, the connection between anabolic 

 (sjmthetic) and catabolic (breakdown) re- 

 actions has been conceived as an energetic 

 one. With the realization that the cata- 

 bolic processes can more or less satisfac- 

 torily be interpreted as the final result of 

 a succession of chemically simple step re- 

 actions, the question of the mechanism of 



