cause there isn't one thing that's going to be 

 important. If there's a little bit lacking of one 

 thing, another will make up for it. That's why 

 I used this model of the ATP-glucose-hexo- 

 kinase system. 



TS'O: That's another question I have. What 

 you're saying is that you have a pretty good 

 idea about how the glucose and the ATP to- 

 gether maintain a stabilizing effect for a steady 

 state. You would think in terms of differentia- 

 tion, however, unless the state is allowed to 

 change its course, presumably the dynamics 

 of the cell would not allow you to jump from 

 one stable state to another. 



B. WRIGHT: Cell wall construction is a 

 big jump. There is no alkali-insoluble ma- 

 terial, and suddenly you've got alkali-insoluble 

 material. Let's just start with cellodextrins. 

 You've got cellobiose in the amoeba. More 

 complex cellodextrins are slowly building up so 

 now you get 6 or 7 glucoses in a chain. It's 

 getting almost insoluble. At the same time 

 G-6-P and UDPG levels are rising. Glycogen 

 is being broken down more rapidly because 

 inorganic phosphate is accumulating, and you 

 get a big build-up of precursors. Trehalose is 

 starting to accumulate, also. Magnesium is be- 

 coming available by the breakdown of something 

 else. All these things occur together at about 

 the same time, buffering each other an inter- 

 acting with each other. When the UDPG level 

 is very low, G-6-P comes to the rescue. There's 

 clear data for that. All these things occur to- 

 gether at about culmination and suddenly we've 

 got the insoluble chains of beta-linked material; 

 and now, the glycogen primer is at a state 

 where it can be used for cell wall synthesis and 

 the enzyme is being transferred, or perhaps is 

 in the cell membrane already. This is pure 

 speculation, but all these things together now 

 give us what we consider to be quite a jump. 

 It's really not a "jump" at all. 



GROSS: Yes, you're goingto see a dramatic 

 change at some point from a system in which 

 the product is soluble to a system in which it 

 is insoluble. 



B. WRIGHT: Right, and this can be a very 

 gradual build-up of ten different things in order 

 to create what we call a very abrupt change. 



CHALKLEY: Wouldn't this, then, suggest 

 that this is a modification of the differentiation 

 process rather than a complete new change from 

 one differentiated cell to another differentiated 

 cell. 



TS'O: Your point seems to be the following: 

 in your system there is a mainstream flowing 



through slowly and it is the accumulation of the 

 stream that gives the momentum for this 

 "abrupt" change. However, I think in many other 

 systems - not being a biologist I couldn't give 

 you specific examples - probably one could have 

 a diversion of the stream, i.e., it can go one way 

 or the other. It is the diversion of the stream, 

 a new choice and not just a continuation, which 

 I would consider a differentiation. 



B. WRIGHT: You have to be more specific 

 or we can't discuss this. 



ZIMMERMAN: How would the antigen sys- 

 tem that we have just discussed relate to this? 



B. WRIGHT: There are differences in en- 

 zyme levels. Alkaline phosphatase, as I said, 

 increases seven-fold. 



EPEL: I think what Dr. Ts'o would like to 

 know is, is there some point when you start 

 initiating this? Is there some earliest point at 

 which you synthesize a real enzyme? 



PAPACONSTANTINOU: Well, aren't you 

 going from a glucose-6-phosphate independent 

 enzyme to a glucose-6-phosphate dependent 

 enzyme? 



B. WRIGHT: The low UDPG level requires 

 the G-6-P. 



PAPACONSTANTINOU: Your culmination 

 stage is very much analagous to the glycogen 

 phosphorylase story in muscle in which one has 

 the regulation starting with the cyclase. It looks 

 like what you've got here is a situation where 

 you may have to go one step further and look 

 for some kind of cyclic -3', 5' AMP which is 

 hormonally regulated. 



B. WRIGHT: Oh yes. An nucleotide levels 

 change also during differentiation. Now, if we 

 could bring in the phosphorylase story which 

 is very much involved, the reactions we've 

 discussed may very well depend on glycogen 

 breakdown. We could make it even more com- 

 plicated. However, I think if we want to discuss 

 the point we shouldn't complicate it further by 

 bringing in more reactions. 



PAPACONSTANTINOU: However, the point 

 is that you've got, also, reaction dependence 

 here. 



B. WRIGHT: Right. There's an intense 

 competition and interaction among all the reac- 

 tions which are going on. 



PAPACONSTANTINOU: My only point is 

 this (I'll try and make it as simple as possible): 

 it appeared to me that you were going from a 

 system in which the enzymes showed more of 

 a substrate independence to a differentiated 

 state in which the enzymes showed more of a 

 substrate dependence. 



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