MUCOPOLYSACCHARIDES OF CONNECTIVE TISSUE 34I 



the cells there and we could always account for the other 95 "o either in the capsular 

 material or in the cell wall. I wonder if you would like to speculate as to why 

 hexosamine-containing substances seem to occur principally outside the per- 

 meability membrane. 



Dorfman: With regard to Dr. Dische's comments I am glad that he did 

 mention this point because there wasn't time to expand on it. As a matter of fact 

 we are at present reinvestigating the question of antigenicity of these substances 

 with the protein complexes which are quite different compounds from alkali- 

 degraded material. We have been able to show in work that I didn't cover (Gross, 

 J. I., Mathews, M. B., and Dorfman, A., jf. biol. Chem. 235, 2889, (i960)) that 

 in vivo the entire protein-polysaccharide complex appears to turn over as a unit. 

 We have measured the metabolism of protein and carbohydrate separately and 

 simultaneously in the same animals and have shown that the rates of turnover are 

 identical for the protein part and the carbohydrate part. This raises some important 

 implications on carbohydrate biosynthesis. With regard to Dr. Rogers' comment, I 

 was careful not to make an absolute correlation between a- and ^-linkages because 

 I don't think that it would hold up. I think that there are other exceptions. ^-Link- 

 ages arise more readily from linear compounds. 



As far as my speculating as to why hexosamine compounds are outside the mem- 

 brane, I suppose I should quote a very famous Swedish teacher I had, Prof. 

 Anton J. Carlson who, whenever asked a question of that kind, said he wasn't 

 there when they made it. I don't know what it is about the chemical properties of 

 hexosamine which is desirable for Nature to incorporate it into structural polysac- 

 charides. Chitin for instance in the insects and fungi, is also a ^-linked glucosamine. 



Mitchell: I wonder if I might speculate a little on why these compounds 

 appear outside, because I am afraid that my remarks earlier about the zip fastener 

 idea were not very clear and were not really understood. Consider a piece of proto- 

 plast membrane as shown in the diagram. It is creating a growing cell wall on the 

 outside and one believes that the precursors are inside, in the cytoplasm and one 

 knows that the cell wall is outside the plasma membrane. The most interesting 

 question is why is the wall made outside and not inside the plasma membrane ? This 

 is a directional matter: why should there be a vector component of the chemical 

 process, seen as a whole ? The simplest way of explaining this would be to say that 

 an enzyme {A) (Fig. i), rather like the ones which Dr. Hestrin is imagining with a 

 sort of hole through it, is accepting the precursors on the inner surface of the 

 plasma membrane and polymerizing them as they pass through to the outside — the 

 polymerized chain becoming extruded as it forms. Such as enzyme, catalyzing a 

 vectorial metabolic process would, of course, have to be specifically located to some 

 substratum in the plasma membrane complex by means of primary or residual 

 bonds. 



As the cell wall is fairly porous, the externally secreted polysaccharides, such as 

 the capsular polysaccharides and the cellulose of Acetobacter xylinum, could be 

 produced and positioned by a similar mechanism. An enzyme polymerizing an 

 extracellular polymer is depicted at B, and the fine chains of the polysaccharide are 

 supposed to be thin enough to go through the holes in the substance of the wall, so 

 that again we would have a vector component of the metabolic process playing a 

 morphogenetic role. This conception is of interest to those trying to relate structure 



