OPTICAL ACTIVITY 101 



TABLE XVIII. 



Ptyalin 6-7 



Invertase - - 4-5 



Maltase acting on maltose 6-6 



methyl-glucoside - 6-2 



Pancreatic lipase 8-0 



Pepsin on proteins 1-5-2 -5 



,, (plastein formation) - 1-0 



Rennin - 5-7 



Trypsin on peptone - 7-7 



gelatin 9-7 



Erepsin - 7*8 



Urease (Decomp. of urea) - - 8-7 



(Synth. )- - 7-0 



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

 rather finical as to what compounds they will attack. Two 

 compounds 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 

 hydrolyse 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 books are similarly placed or 

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

 axis A C by 180. If, after passing through book one, the strip 

 of metal is given a twist, then book two will have to be turned 

 through a corresponding angle before the metal will slip through 

 its pages. The rotation of book two may be taken as an index 

 of the twisting of the plane of the metal strip. Various factors 

 may modify this twisting : 



(a) The nature of the metal. The same twisting force would 

 produce very different results in, say, copper and steel. 



(b) The length of the strip exposed to the twisting force. The 

 longer the strip between Bl and B2 the greater will be the 

 twisting, other conditions being equal. 



