D. R. HOAGLAND 



environments. To what extent, if at all, the relative proportions of 

 amylose and amylopectin may be subject to modification by physio- 

 logical conditions remains to be studied. 



The phosphorolytic mechanisms probably will supply the key 

 to an understanding of the synthesis of another carbohydrate almost 

 universally synthesized by higher plants, namely, sucrose. This is also 

 the dominant sugar of commerce and, as one authority has pointed 

 out, is manufactured commercially in far greater quantity than any 

 other pure chemical product. It is natural, therefore, that many at- 

 tempts have been made to analyze the mechanism of sucrose synthesis 

 in the plant. Recently the enzymic synthesis of sucrose in vitro was 

 accomplished (7); and, while the enzyme system responsible is 

 derived from a bacterial organism (Pseudomonas saccarophila), the 

 achievement has such great suggestive interest for the investigator of 

 the nutrition of higher plants that it seems appropriate to mention it 

 in this connection. The substrates utilized in the synthesis were glu- 

 cose-! -phosphate and fructose. Sucrose is broken down into these 

 components in a phosphorolytic reaction catalyzed by an enzyme 

 system in the bacterial cell. By starting with glucose-1 -phosphate 

 and fructose in the presence of the enzyme, pure crystalline sucrose 

 was prepared which was identical with the natural product. The 

 identity was established by all available physical and chemical criteria. 

 This is the first well-authenticated synthesis of this sugar. 



It is true that a similar enzyme system has not yet been iso- 

 lated from the tissues of higher plants, despite various attempts to do so 

 in this laboratory. Nev^ertheless, biochemical studies on various species 

 of plants strongly support the view that the synthesis of sucrose does 

 proceed by chemical reactions in which glucose or fructose phosphate 

 esters, or both, serve as substrates, although the mechanism is probably 

 not identical with that of the bacterial enzyme system. Certain studies 

 on sugar cane leaves suggest that, in the higher plants, fructose di- 

 phosphate takes part in the synthetic reaction (6). It is of funda- 

 mental importance that the experimental evidence now available 

 shows that, for the synthesis of sucrose from glucose and fructose in the 

 plant, aerobic metabolism is indispensable. Possibly aerobic oxida- 

 tions are essential to the phosphorylation of one of the substrates in- 

 volved in the synthesis of the sucrose. The question is complicated by 

 the observation that various substrates other than glucose and fructose 



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