ENZYMES 135 



thesis, and if so what are they? All these problems lead to smaller 

 problems and ramifications of their own. 



At present the matter of timing in the combination of the compo- 

 nent amino acids is not established. Some experimental results suggest 

 I hat intermediate peptides do not appear. All the peptide bonds must 

 be formed practically simultaneously. Moreover, when a compound 

 is added to the system preventing incorporation of one kind of amino 

 acid into enzyme, none of the other amino acids are combined. On 

 the other hand, experiments with different cells and enzymes and by 

 different investigators contradict the above interpretation. Although 

 it has been assumed that different organisms synthesize their proteins 

 in the same way, perhaps they do not. Or maybe different enzymes 

 arise by imrelated routes. 



Ribonuclease catalyzes the partial hydrolysis of ribonucleic acids 

 into the individual nucleotides. This widely distributed enzyme has 

 been isolated and extensively studied to ascertain the chemical and 

 physical similarity of the enzymatically active individual molecules. 

 Ribonuclease from a single source can be separated into two fractions, 

 one of them small in quantity, both with catalytic activity. Perhaps 

 the one fraction is an artifact of isolation. At any rate, incomplete 

 structure studies on the predominant fraction make it most probable 

 that all the molecules of this particular principal enzyme fraction are 

 alike, even to identical sequences of amino acids in the peptide chain. 

 Thus there are highly preferred structures for enzymes, although 

 there may occasionally be more than one kind. 



How can such preference be expressed during enzyme biosynthesis? 

 Some organisms can make a particular enzyme and some cannot. 

 Experiments involving both enzyme synthesis and genetics show that 

 the former is under hereditary control. Special techniques modifying 

 the heredity of a cell can remove or introduce the capacity for the 

 formation of one of a variety of enzymes. This relationship then ties 

 the biosynihesis of enzymes to hereditary in general. More specifically, 

 the use of inhibitors acting on the nucleic acids blocks all enzyme 

 synthesis. In addition, a cell deficient in the ability to make a par- 

 ticular enzyme gains this ability when properly treated with deoxyribo- 

 nucleic acid extracted from cells related to the deficient cell but 

 possessing the synthetic capacity missing from such cells. Hence this 

 type of nucleic acid is important in the control of enzyme synthesis. 

 Moreover, similar experiments make deoxyribonucleic acid the basis 

 of heredity in general. 



Although required, deoxyribonucleic acid is not the only essential 



