146 



THE CELL AND PROTOPLASM 



All the yellow ferments are, as it seems, 

 rather similar in the matter of external 

 properties, such as molecular weight, ab- 

 sorption spectrum, and flavin content. The 

 purest preparation of the old yellow fer- 

 ment contained 0.65 per cent flavinphos- 

 phate. Haas's ferment contained 0.7 per 

 cent, and Straub's purest "coenzyme fac- 

 tor" contained 0.65 per cent. Ball's 

 xanthinoxidase 0.63 per cent. The major- 

 ity of the yellow ferments resemble the old 

 one in so far as they are only slightly dis- 

 sociated. Only amino acid oxidase is so 

 strongly dissociated that it could not be 

 prepared as such, and the prosthetic group 

 and the protein component each had to be 

 prepared separately. 



In the matter of function, all the yellow 

 ferments resemble one another in that they 

 transfer hydrogen; the differences lie in 

 the source of the hydrogen, where they 

 transfer it, and in the speed with which 

 this takes place. 



It is a striking fact that some of the 

 flavin ferments (and, so far as it is known, 

 all of the pyridine-nucleotide ferments) are 

 largely dissociated, while others of the 

 flavin ferments are practically undissoci- 

 ated into prosthetic group and protein at a 

 physiological pH value. So far as we know 

 it seems to be a general rule that the en- 

 zymes which react directly with the sub- 

 strates are greatly dissociated, such as the 

 pyridine ferments and the flavin ferment 

 acting as (?-amino acid oxidase, whereas the 

 intermediate catalysts, such as the flavo- 

 proteids taking their hydrogen from dihy- 

 dropyridine, or the cytochromes, or the 

 oxidases are undissociated. I think we may 

 find this arrangement by nature to be very 

 remarkable. The ability of the living cells 

 to make different proteins seems to be un- 

 limited, whereas animal cells cannot syn- 

 thesize most of the prosthetic groups, e.g., 

 thiamin, flavin, and nicotinic acid amide. 

 This is the reason why these have to be 

 taken up by the animals from plants and 

 have the character of vitamins. Now, the 

 animal cells have to transform a great 

 variety of substances, such as sugars, amino 

 acids, lactic acid, pyruvic acid, and so 



forth. It seems perfectly possible that the 

 cells make one specific protein for each 

 of these substrates. Some few prosthetic 

 groups can then form dissociable enzymes, 

 one time with one protein and again with 

 another, thus picking up hydrogen from 

 different protein-substrate compounds much 

 as a bee picks up honey from different 

 flowers. 



The hydrogen from different substrates 

 may then enter the main highway of com- 

 bustion, where a stream of hydrogen from 

 the substrate side meets a stream of elec- 

 trons from the oxygen side with subsequent 

 formation of water. The intermediate 

 catalysts in this highway have no reason for 

 dissociation: they take electrons or hydro- 

 gen always from one certain catalyst, giving 

 these to another. 



If, finally, we summarize our present 

 knowledge about phosphoric acid ester com- 

 pounds with proteins, we shall find a great 

 many highly important substances belong- 

 ing to this group. I have already mentioned 

 ferments consisting of nucleotide proteids 

 (flavin- and pyridine-proteids). These are 

 beyond doubt the most important of the 

 enzymes involved in delivering energy, be- 

 cause they may be used both in oxidation 

 and in fermentation. They are present 

 everywhere from the higher animals to the 

 anaerobic bacteria, which have no hemin 

 proteids because they do not need them. 



If we consider further that the cell 

 nucleus, the chromosomes, and the genes 

 consist of nucleotide proteids, as well as the 

 viruses, we can perhaps arrive at the con- 

 clusion that living material arises from 

 dead when nucleotides are coupled with pro- 

 teins. There has been much discussion 

 about whether the viruses are living or dead, 

 and generally about the limits between liv- 

 ing and dead materials. As far as I can 

 see there is no more sense in such a discus- 

 sion than in, for example, Descartes' 

 theory that the soul has its seat in the 

 pineal gland. But it could perhaps be 

 worth while to point out the analogy be- 

 tween the viruses and the metal-free fer- 

 ments transporting hydrogen : both are 

 built up of nucleotides plus protein. 



