Molecular Structure in Protoplasm 73 



zymes in this case, are fairly well known (64) . The larger complex 

 is thought to consist of several different enzymes which function in 

 a series, one reaction following another in more or less gradual steps 

 leading eventually to the disintegration of glucose. Each of the en- 

 zymes consists of a protein molecule and a prosthetic group. The 

 prosthetic groups, at least several of them, are known; and of the pro- 

 tein, the molecular weights of some are known, but little more in- 

 formation is available concerning them except that they are specific 

 for their particular prosthetic groups. The steps in the disintegration 

 process are known to some extent although not completely; we know 

 the materials which go into the machine and the details of a consider- 

 able amount of the disintegration as well as the final products; thus 

 here we have the parts of the machine and know how they perform 

 by themselves, but we do not know how to put them together to form 

 the complete structure; that is, we are ignorant of the arrangement 

 of the small mechanisms in the complex as a whole. 



Recent evidence makes it seem probable that these small respira- 

 tory mechanisms may be associated with still other small mechanisms 

 to carry on even more complex activities. For example, the presence 

 of copper and iron along with chlorophyll, proteins, and lipoids has 

 been shown in isolated, intact chloroplasts (119, 120), thereby in- 

 dicating that respiratory mechanisms are probably associated with 

 photosynthetic mechanisms in the minute chlorophyll-containing 

 portions. Concerning this synthetic process we know with a con- 

 siderable degree of certainty that the raw materials which go into the 

 machine are carbon dioxide and water and that the products which 

 come out are glucose and oxygen; and we know here also the mole- 

 cular nature of part of the machine, the energy-absorbing chloro- 

 phyll molecule and in general the protein chain. This is a step in 

 advance of the leucoplast where the material going in, glucose, and 

 that coming out, starch grain, are known, but concerning the mole- 

 cular structure of the machine, practically nothing is known except 

 that it probably is mainly protein. In contrast to the chloroplast, 

 however, here the end product, the starch grain, is microscopically 

 visible. 



In the microscope we see a leucoplast as a complex mechanism, 

 but as though at a great distance, for the details are invisible, al- 

 though the output of starch grain is seen. Here we see a mechanism 

 as a whole but know nothing of the smaller component mechanisms 

 or of their molecular details. By taking the starch grain apart we 

 have learned that the mechanism is capable of condensing glucose 



