TABLE ni 

 Fractionation of Radioactive Cell Wall Material with Schweizer's Reagent 



Total cpm 

 Exp . Original Undissolved Frac . A Frac . B Frac. B % Total 



TABLE IV 

 Hydrolysis of Fractions A and B 



.012 



Sample 

 Oyster glycogen 

 Oyster glycogen 

 Non- radioactive Frac. 

 Non-radioactive Frac. 

 Radioactive Frac. B 

 Radioactive Frac. A 



Enzyme Treatment 



<-l,4-phos- amylo- 1 , 6-gluco 



phorvlase sldase 



present 

 present 

 present 

 present 

 present 

 present 



absent 



present 



absent 



present 



absent 



absent 



7, Hydrolysis 

 38 

 100 

 41 

 90-100 

 100 

 60-80 



terial is composed not of cellulose only, but 

 rather of a 50-50 mixture of cellulose and 

 glycogen polysaccharides in intimate associa- 

 tion. During synthesis of this material in vitro 

 most of the radioactive glucose in UDPG-^'*Cis 

 incorporated into the glycogen polymer (5). 



Let us now turn to some properties of the 

 enzyme system catalyzing the synthesis of cell 

 wall material from UDPG (Fig. 6). We deter- 

 mined the activity of the enzyme as a function 

 of UDPG concentration. The UDPG concentra- 

 tion does not change significantly during poly- 

 saccharide synthesis in vitro in the presence 

 of a well-washed particulate preparation. There- 

 fore it seems justified to consider 1.3 x 10"^ to 

 be the approximate K^, for UDPG in the synthesis 

 of cell wall material. During differentiation in 

 the slime mold the intracellular concentration of 

 UDPG is well below 10-3 M except in culminating 

 cells which are rapidly accumulating cell wall 

 polysaccharides. Assuming that the UDPG values 

 approximate the concentration available to the 

 enzyme in vivo, it would appear that UDPG is 

 one limiting factor to the initiation of cell wall 

 synthesis in the differentiating cell. Conversely, 



I 10 100 



UDPG ( p MOLES /ml x 10) 



Fig. 6. 



From Wright, Barbara E.: Control of Carbohydrate 

 Synthesis in the SUme Mold. In Developmental and Meta- 

 bolic Control Mechanisms and Neoplasia (A Collection of 

 Papers Presented at the Nineteenth Annual Symposium 

 on Fundamental Cancer Research, 1965), p. 311. Balti- 

 more, The Williams and Wilkins Company, 1965. 



the depletion of UDPG, which occurs very rapidly 

 during sorocarp construction, would of course 

 be a determining factor in the termination of 

 polysaccharide synthesis. 



Both glucose-6-phosphate and magnesium 

 stimulate cell wall polysaccharide synthesis 

 in vitro (Table V). G-6-P is known to lower the 

 Km for UDPG in a number of other systems in 

 which glycogen synthesis has been studied. If 

 one adds magnesium extracellularly in the 2% 

 agar in which the slime mold is differentiating, 

 it increases the rate of overall differentiation 



113 



