342 ALBERT DORFMAN AND SARA SCHILLER 



to function, I think, because it suggests a connection between morphogenesis and 

 the unique asymmetry of protein molecules. 



Dorfman: I like this very much and there isn't time to expand on it. Last year 

 we proposed a mechanism for polysaccharide synthesis which envisaged a mechan- 

 ism of this kind. One of the difficulties is that we find no low-molecular weight 

 intermediates. We have to think of an enzyme which somehow or other forms 

 hyaluronic acid on the enzyme while the chain keeps getting longer until it is large 

 enough and then is detached from the enzyme. 



Hestrin : In our laboratory Schramm and Zelinger have found that /3-glucose-i- 

 phosphate can be condensed in the presence of maltose phosphorylase with 

 glucosamine to afford in good yield the ot-glucosyl-i,4-glucosamine. They have 

 also obtained similarly the acetylglucosamine derivative. These materials are thus 



Cytoplasm 



Plasma membrane 



Medium 



Cell wall polymerizing enzyme ""Xl-s:*^^^ 



^"v aJ 



Cell wall precursors — ^^=*'^ 



Extracellular polysaccharide precursors _ ^^ 



NO 



Extracellular polysaccharide ' ^■^=t^-' 



polymerizing enzyme 



Extracellular 

 polysaccharide 



Fig. I. 



now readily available and may be useful for studies designed to elucidate the effect 

 of an a-linkage on the properties of glucosamine-containing polymers. 



A general comment concerning the interpretation of data obtained in enzyme 

 solution on a substrate of a saccharide synthesis might perhaps be appropriate. 

 There is a tendency to take the view that a demonstration of synthesis in an en- 

 zyme solution suffices to demonstrate that the substrate in question is also the 

 physiological substrate. However, especially if the reaction observed in a solution is 

 sluggish, an observed reaction may be only an artifact. Some of the uridine 

 diphosphoglycoses, for example, can still conceivably merely be analogues of 

 unidentified physiological substrates. Before accepting a particular polymer syn- 

 thesis reaction as having been demonstrated, we should insist on a realization of the 

 reaction under conditions in which there occurs a net increase of the mass of the 



