Conjugated Proteins 73 



impress individuality and specificity on cells or cell communities. One 

 could venture the opinion that biochemical evolution is accompanied, or 

 indeed caused, by the formation of macromolecules of ever-increasing 

 complexity composed of an ever-diminishing number of constituents. 

 One mechanism by which this may be accomplished is that of conjuga- 

 tion. Many different conjugated proteins are being recognized, such 

 as the nucleoproteins, the lipoproteins, the mucoproteins, or the chromo- 

 proteins; many enzymes that carry cofactors, distributed in specific 

 positions on the protein molecule, belong to one or the other of these 

 groups. But we encounter also lipopeptides, mucolipides, etc.; and 

 many more unrecognized compounds of this type must daily be going 

 down the drains of our laboratories than repose in the graveyards of 

 our scientific journals. When I am sometimes told that biochemistry 

 has "run out of good problems," I shudder and reply: "Biochemistry 

 has not even begun!" 



The general aspects of the problem of conjugation have rarely been 

 formulated clearly. This is perhaps not surprising, for this class of 

 substances has long found itself between two chairs, as it were: too 

 big to be handled conveniently by the chemist; too small to be seen 

 consistently by the morphologist. The chemist strove for the isolation 

 of the smallest unit endowed with homogeneity ; the biologist attempted 

 the recognition of the simplest structure endowed with function. The 

 prize went to the loudest prophet with monomaniac intent. Since 

 scientists in our time have, on the whole, lost the ability to say "We 

 don't know," it is usually the man with the premature explanations 

 that brings home the bacon; and by the time he has been found out 

 he will have devoured it. 



Another obstacle to the recognition of the biological importance of 

 the conjugated proteins may be seen in their being usually considered 

 apart from each other under the headings of their respective prosthetic 

 groups. I am aware of only one instance, namely, in a symposium held 

 some time ago (1953) at Rutgers University, in which an attempt was 

 made to consider the conjugated proteins as a family of substances 

 having more in common than the small print that they occupy in the 

 current textbooks of biochemistry. But there can be little doubt that 

 many, if not all, life processes take place on what may be considered the 

 surfaces of conjugated proteins. It is, perhaps, not uninstructive very 

 briefly to compare two groups of conjugated proteins on which my 

 laboratory has spent some effort, viz., the nucleoproteins and the lipo- 

 proteins. 



