332 Discussion 



in the synthesis of RNA and whether the rise in RNA and the increase 

 in phosphatase content might not be closely connected. The two curves 

 are not the same, but they are similar. 



Magasanik: Levinthal's results would not support this idea: he 

 obtained mutants which could not form phosphatase, and which grow 

 very well in a medium containing inorganic phosphate, but had lost the 

 ability to grow in media containing an organic phosphate compound as 

 the sole source of phosphate. Apparently this particular phosphatase is 

 not essential for growth. 



Hinshelwood: The conditions of formation of the two might be similar. 



Lehninger: This discussion reminds me of our discussion yesterday 

 about the requirement of inorganic phosphate to get things going. Like 

 many enzyme chemists, I have often wondered about the role of alkaline 

 and acid phosphatase in cells. Dr. Racker (1955, Physiol. Rev., 35, 1) 

 made the interesting suggestion that they are possibly artifacts; that 

 they may be expressions of the activity of some polyfunctional enzyme, 

 like triose phosphate dehydrogenase which we know can split acetyl 

 phosphate, for example. In this connexion, can he say whether this 

 enzyme has ever shown the ability to split 1 : 3-diphosphoglycerate, 

 because it might be possible to find an explanation of what phosphatase 

 activity is doing in the cell. 



Racker : We are quite certain of the acylase activity of triose phosphate 

 dehydrogenase in respect to acetyl phosphate. We also know that the 

 acyl enzyme formed with 1 : 3-diphosphoglycerate is quite unstable in 

 the presence of DPN. But I would hesitate to give an accurate evalua- 

 tion of the rate of cleavage of 1 : 3-diphosphoglycerate by the enzyme, 

 because of the rather rapid spontaneous hydrolysis of this compound. 

 I like the suggestion that phosphatases may serve as regulators of intra- 

 cellular phosphate concentration and I had something similar in mind 

 earlier when I discussed the possible role of ATPase in allowing the 

 Krebs cycle to go on under conditions of ATP over-production (see 

 p. 215). Dr. Magasanik, do the phosphatase-deficient mutants require 

 relatively high concentrations of inorganic phosphate for growth? 



Magasanik : They require the usual amount. If the inorganic phos- 

 phate is replaced by glycerol phosphate, then the mutant cannot grow. 

 If there is more than one phosphatase, then this one seems to be the 

 important one. 



Potter : That is the important point : there is more than one phospha- 

 tase. A discussion of phosphatase is one of the most embarrassing 

 subjects for a biochemist, and until we know what phosphatases we are 

 discussing, the discussion is not likely to be very useful. It may turn 

 out that some of the enzyme activity which is called phosphatase may 

 have something to do with protein synthesis. We must wait until the 

 current studies on protein synthesis are correlated with phosphatase 

 activity. I am sure that the studies to which Dr. Magasanik referred do 

 not result in the production of cells which have no phosphatase activity. 



Magasanik: Levinthal's results indicate that unless the cells have this 

 particular phosphatase, they do not have either the right enzyme or 

 enough enzyme to be able to produce sufficient inorganic phosphate 



