these biochemical interactions are intimately 

 associated with the genetic regulation of mor- 

 phogenesis. To be more specific, we would like 

 to know whether y-crystallin synthesis is in- 

 timately linked to fiber cell formation and 

 whether the r-crystallins are required to bring 

 about the formation of a fiber cell. The poten- 

 tial for synthesizing y-crystallins is inherent 

 in the genome of the cell. This part of the 

 genome is non-functional in the epithelial cell. 

 Can these genes be activated without bringing 

 about a simultaneous (a) cellular elongation; 

 (b) loss of cellular replication (c) stabilization 

 of m-RNA and (d) breakdown of the ribosomes? 

 The degree of coupling or uncoupling of tissue 

 specific protein synthesis to morphogenesis is 

 an important part of the mechanism of cellular 

 differentiation. We feel that we have now reached 

 the stage where we can begin to answer these 

 questions. 



MASSARO: I have a couple of questions if 

 you wouldn't mind going back to LDH. What 

 other data do you have besides the pyruvate 

 inhibition curves to show that the LDH-1 of your 

 lens system is different from the LDH-1 of the 

 skeletal muscle, heart, brain, glands system? 



PAPACONSTANTINOU : Well, we don' t have 

 any other evidence. 



MASSARO: Recently we've found that in 

 fish the LDH system of the eye apparently 

 differs from the skeletal muscle, heart, glands 

 and CNS system. I would be kind of shaky about 

 making a very strong statement concerning the 

 results Cahn got in tissue culture and the results 

 one obtains with aging muscles because we just 

 don't know much about what goes on during the 

 aging process. Also, there are dedifferentia- 

 tion and other problems in tissue culture. 



GROSS: Did you say that the behavior of 

 your LDH-1 with respect to pyruvate was 

 different from muscle LDH? 



PAPACONSTANTINOU: No, it's the same. 

 We have no evidence that they' re different at all. 



MASSARO: Doesn't your LDH-1 differ from 

 the LDH-1 of the muscle tissue? 



PAPACONSTANTINOU: No, it's the same; 

 it's sensitive to pyruvate. The difference is that 

 the fiber cells retain LDH-1 although they have 

 a high rate of aerobic glycolysis, and they should 

 have LDH- 5. 



MASSARO: Are all of the properties of 

 this LDH-1 similar to the LDH-1 of the muscle? 



PAPACONSTANTINOU: They are similar 

 to those of the heart muscle. 



MASSARO: The only difference is that in 

 this particular environment you have an LDH-1 



which is sensitive to a clearly known pyruvate 

 concentration? 



PAPACONSTANTINOU: That's right. What 

 we're trying to point out here is that the fiber 

 cells are highly glycolytic and according to 

 the theory that's been proposed for heart and 

 skeletal muscle, the fiber cells should retain 

 LDH-5; instead they retain LDH-1. 



MASSARO: Then, the only difference that 

 you see here is in the pyruvate inhibition 

 curves? 



GROSS: The proposal about LDH and the 

 oxidative level is, as I understand it, not a 

 theory, but an explanation of why you have 

 more of one enzyme in one tissue than another. 

 You are suggesting that differential gene action 

 results from the influence of the environment 

 of the cell. In the classical cases, the influence 

 was pinpointed as oxygen tension or as the state 

 of carbohydrate metabolism. Now, as I under- 

 stand it, Papaconstantinou's evidence showed 

 that, in his system, this explanation is invalid. 

 My conclusion from that would be that the 

 initial explanation is not universally applicable. 



MASSARO: This conclusion is on the basis 

 of the pyruvate inhibition? 



GROSS: Yes. 



PAPACONSTANTINOU: It's based on the 

 fact that LDH-1 persists in a highly glycolyzing 

 system that can go into oxygen debt. 



MASSARO: You see, I think we're running 

 into some semantic problems here by labeling 

 this LDH-1. 



PAPACONSTANTINOU: WeU, I can't call 

 it heart-type LDH because it's not in the heart. 



MASSARO: We're crossing over systems 

 and using the LDH terminology of the heart 

 and skeletal system in the eye system. I don't 

 think this is valid because I don't think they're 

 comparable. I think, perhaps, from this data 

 that the eye LDH system may be quite different 

 from that of skeletal muscle and heart muscle. 



GROSS: What you're saying, then, is that 

 there are, in fact, different cistrons involved. 



MASSARO: That's right. 



GROSS: The initial assumption in this story 

 was that there are two genes involved and they' re 

 the same in every genome. Now, you're sug- 

 gesting, in fact, that there are other genes 

 involved. 



MASSARO: We know this for a fact in the 

 case of the so-called "X-bands of gonadal LDH" 



PAPACONSTANTINOU: I would not expect 

 to find differences in amino acid composition 

 between lens LDH and heart LDH from the same 

 animal. Genetically the two LDH's should be 



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