126 



ENZYMES 



employed the point of equilibrium is shifted towards isomaltose. 

 The whole subject requires re-examination from the point of 

 view of colloid chemistry, especially with regard to the influence 

 of P^ on activity. The following table gives the optimum P^ for 

 certain enzymes : 



TABLE XXII. 



Much has been made of the fact that enzymes seem to be rather 

 finical as to what compounds they will attack. Two compoimds 

 may exist side by side similar except in one respect. They 

 may differ in structure as the right hand differs from the left. 

 That is, the one compound is structurally a mirror image of the 

 other. The enzyme selects one for attention and hardly looks 

 at the other. If the enzyme is engaged in synthesis, it invariably 

 builds right-handed sugars and left-handed leucine (an amino acid). 

 If engaged on demolition, the enzyme will hydrolysc all or nearly 

 all of the right-handed sugar before touching its mirror image, and 

 similarly with /-leucine. How can this be explained ? 



Optical Activity. 



It is obvious that a paper-cutter or strip of metal can pass 

 through a book only in the plane of the pages, and may pass 

 through a second book when both liooks are similarly placed or 

 when one has been placed upside down, i.e. rotated on its central 

 axis AC by 180° (Fig. 28). If, after passing through book one, the 



Fig. 2S. — Model of polariinet.er. ^ = source of liylit, i>'i = polari8er, /) = point at which 

 twisting force is applied, B.. analyser, the amount of twisting at D can be estimated from 

 the angle through which B. has to be rotated to allow of the passage of the metal strip AC, 

 C = eyepiece. 



