314 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES III 



For amylopectin of Ys million molecular weight (Table XXVIII, 

 p. 311), which corresponds to a degree of polymerization of 2000, 

 64 bifurcations and as many end members would be found. The 

 average length of the branches with 1 5 glucose units would measure 

 about 50 A, so that the brush-like molecule of Fig. 155b would cover 

 350 A in an expanded state. 



The amylopectin content varies in the different kinds of starch, 

 which accounts for the familiar specific differences between them. 

 Potato starch has a higher amylopectin content than wheat starch 

 (Meyer and Bernfeld, 1941b). Ketan, the starch grains of which 

 are dyed red bv iodine, contains only amylopectin of high molecular 

 weight (Meyer and Heinrich, 1942). Amylopectin possesses weakly 

 acid properties and can therefore be separated by electrophoresis from 

 amyloses, which are absolutely neutral (Lamm, 1937). Presumably the 

 acid groups in amylopectin are responsible for the fact that only basic 

 dyes can stain starch grains with a colour which is fast to washing, 

 Samec (1927) says they consist of phosphoric acid. Meyer and Mark 

 questioned in 1950 the existence of phosphoric ester bridges between 

 the glucose chains, and nowadays amylopectin is regarded as free 

 from phosphoric acid (Meyer and Brentano, 1936; Samec, 1942), 



The discovery by Hanes (1940) that the enzymatic degradation of 

 starch is a phosphorolysis, and not hydrolysis, invests the phosphorus 

 content of starch grains with a particular significance. This knowledge 

 led to the synthesis of starch in vitro. Starting from phosphorylized 

 glucose, Hanes united it with the enzyme phosphorylase ; when equi- 

 librium sets in between glucose- 1 -phosphate and starch, this com- 

 pound, owing to its insolubility, is synthesized. Hanes' synthesis of 

 starch is the first instance of an artificial manufacture of a high 

 polymeric natural product. 



The decomposition of starch is a highly complicated process of 

 fermentation (Myrback, 1938; Myrback and co-workers, 1942). 

 Amylase, the enzyme which decomposes starch, consists of two 

 different constituents, viz., the dextrinogenous a-amylase and the 

 saccharogenous /9-amylase, both of which have been isolated and 

 crystallized (Meyer, Fischer and Bernfeld, i 947 ; Meyer, Fischer 

 and PiGUET, 195 1 ; Meyer, K, H,, 195 i). The latter splits off maltose 

 (twin groups of glucose) from the aldehyde end of the starch chains 

 (Fig. 152b, p. 311), but is unable to break up the branch junctions 



