Simple Laboratory Experiments on Leaf Pigments. 33 



The compounds formed by the magnesium free derivatives 

 with other metals are unstable towards acids, and require other 

 conditions for their formation. Thus phytochlorin e in methyl 

 alcoholic solution gives, with water-free barium hydroxide in excess, 

 a barium compound. Even compounds with the alkali metals can 

 be formed in a similar way, the compounds with potassium being 

 the least stable of them all. 



The magnesium compound occupies a place in the middle of 

 the series as regards stability, the two extremes being the copper 

 and potassium compounds. 



Experiment 10. The action of chlorophyllase. 



Fresh leaves of a species rich in chlorophyllase (Heracleum, 

 Galeopsis) are finely divided and put in a 70% acetone solution, 

 3 c.c. of solution being used for every gram of leaf powder. The 

 chlorophyll, by means of the chlorophyllase, is dissociated into 

 phytol and the acid chlorophyllide. This can be demonstrated 

 after about a quarter of an hour if the solution is diluted with water, 

 transferred to ether and shaken with 0'05% sodium hydroxide. The 

 sodium hydroxide takes up more colouring matter the further the 

 enzyme action has progressed. 



Experiment 11. Destruction of chlorophyllase. 



If fresh leaves of a species rich in chlorophyllase are first 

 steeped in boiling water for a few minutes before they are placed in 

 the acetone solution, unaltered chlorophyll is extracted which does 

 not react with dilute alkali. 



The action of the enzyme chlorophyllase consists in either an 

 alcoholysis (in alcoholic media) or hydrolysis (in aqueous media). 

 For instance, in methyl alcoholic media, the phytyl group is 

 replaced by a methyl group according to the equation 



(Ca^Hs.ON.Mg) (COOCH3) (COOC,oH3,) + CH30H = 



C.oHssOH + (C3,H3oON,]Wg) (COOCH3) (COOCH3). 

 Phytol. IVIethyl chlorophyllide. 



In aqueous solutions hydrolysis takes place with the formation of 

 free acid chlorophyllide 



(C3„H3oON*Mg)(COOCH3)(COOC,„H,,) + H30= C.^Hg^OH 



+ (C3,H3oON,]Vlg)(COOCH3)(COOH). 



Chlorophyllide. 



Experiments 10 and 11 demonstrate the hydrolysis of chlorophyll 



and also indicate that it is an enzyme action. Chlorophyllase is a 



c 



