324 SHLOMO HESTRIN 



of the pentose cycle to contend with. There existed a fairly close agreement between 

 a pattern predicted on the basis of a schematic pentose cycle and the actual findings. 



DoRFMAN : The first part of your paper might be of interest in this question 

 of specificity of the aglucone or glucone of glucosidase. Dr. Julio Ludowieg has 

 recently studied this problem with Dr. Vennesland and myself using ^*0 with 

 the hyaluronidases. In the case of the streptococcal hyaluronidase, as some of you 

 know, the product is an unsaturated compound. Presumable this is an elimination 

 reaction and, as one might have guessed, no incorporation of ^*0 from the medium 

 occurs during this hydrolysis. The cleavage is thus of the ether rather than the 

 glycoside link. With testicular hyaluronidase, which is a conventional glucosidase, 

 "O incorporation apparently occurs, the cleavage is thus apparently of the glyco- 

 side bond. Testicular hyaluronidase does not act on chondroitin sulphuric acid 

 B which contains L-iduronic acid instead of D-glucuronic acid but it does act on 

 both hyaluronic acid and chondroitin sulphuric acid A, one of which has glucos- 

 amine and the other has galactosamine. Thus the specificity does not reside in the 

 glycone portion of the molecule. 



Hestrin : Such cases encourage the consideration of the possibility that the 

 interaction of enzyme and sugar does not exclusively involve one side of the sugar. 

 Conceivably the substrate has to be fitted into a pit on the protein surface, or per- 

 haps, as Wallenfels has conjectured, the protein winds itself around the substrate. 



Mitchell: I would like to ask Dr. Hestrin a question stemming from his last 

 remarks. It seems as though the specificity of some of these enzymes implies that 

 there may be a hole into which the precursor goes and out of which the polymer 

 has to be extruded. Now, could I preface my question by saying that about five 

 years ago. Dr. Moyle and I discovered that in certain micrococci there was an 

 autolytic system that seemed to be capable of cutting a ribbon out of the spherical 

 cell wall so that it would fall readily into two hemispherical parts ; and this system 

 seemed to be mechanically attached to the wall, for it centrifuged with the cell 

 wall fraction of disintegrated cells and could not readily be washed oflF. We made 

 the suggestion that this system might be a synthetic system, and we visualized the 

 synthesis as though the enzymes were like the clasps on a set of zip fasteners fixed 

 in the plasma membrane and the zips, representing the unpolymerized cell wall 

 precursors, we imagined as being pushed through from the inside to become 

 zipped together, forming a wall on the outside. Now, could I ask in that context, 

 whether you know where the particles come from in your particulate preparations ? 

 Is it at all likely that they are originally part of the plasma membrane, and if so, 

 do you think perhaps a precursor is being pushed out which is not actually visible 

 yet as a fibre ? 



Hestrin: The particles could be fragments of the cell wall; we don't know. 

 If they are fragments of the cell wall we could be more confident that the observed 

 incorporation activity truly represented a polymerization process leading to fibre 

 production. If the particles are of an endocellular origin, it is difficult to see how 

 they could have operated in vivo to give rise to extracellular deposition of fibre. 

 Perhaps, in that case, the observed incorporation of radioactivity was only a mani- 

 festation of an oligorepetitive rather than of a polyrepetitive process of trans- 

 glycosylation. 



If we assume that the polyrepetitive step in synthesis occurs at the cell membrane 



