84 THE FATS AND UPASES [CH. 



Expt. 86. Reactions of fatty adds, (a) Try the solubilities in ether and alcohol 

 of the acids from the previous experiment. They are soluble, (b) Shake an alcoholic 

 solution of the fatty acids with dilute bromine water. The colour of the bromine is 

 discharged owing to the bromine forming additive compounds with the unsaturated 

 acids. 



The question of the metabolism of fats in the plant is a very com- 

 plicated one and has not yet been satisfactorily investigated. All plants 

 may have the power of synthesizing fats, and a great number, as we have 

 seen, contain large stores of these compounds in the tissues of the 

 embryo, or endosperm, or both. The point of interest is that of tracing 

 the processes by which these fats are synthesized, and are again hydro- 

 lyzed and decomposed. The products of decomposition may serve for 

 the synthesis of other more vital compounds as the embryo develops, 

 and before it is able to synthesize the initial carbohydrates, and to 

 absorb the salts requisite for general plant metabolism. 



One fact seems fairly clear, namely that when fat-containing seeds 

 germinate, an enzyme is present in the tissues which has the power of 

 hydrolyzing fats with the formation of fatty acids and glycerol. Such 

 enzymes are termed lipases. 



The lipase which has been most investigated is that which occurs in 

 the seeds of the Castor-oil plant (Ricinus communis). It has been shown 

 that if the germinating seeds are crushed and allowed to autolyze 

 (p. 19) in the presence of an antiseptic, the amount of fatty acid in- 

 creases, whereas in a control experiment in which the enzyme has been 

 destroyed by heat, no such increase takes place (Reynolds Green, 9, 10), 

 Investigation has shown the enzyme to be present also in the resting 

 seed, but in an inactive condition as a so-called zymogen (Armstrong, 

 4, 5, 6, 7). The zymogen is considered to be a salt and, after acidifica- 

 tion with weak acids, the salt is decomposed, and the enzyme becomes 

 active. After the preliminary treatment with acid, however, the enzyme 

 is most active in neutral solution. The effect of acid on the zymogen 

 may be demonstrated by autolyzing the crushed seed with a little 

 dilute acetic acid ; the increase of acidity will be found to be much 

 greater than in the case of a control experiment in which acid has not 

 been added. 



It has not been found possible to extract the enzyme from the 

 resting seed. An active material can be obtained by digesting the 

 residue, after extraction of the fat, with dilute acetic acid and finally 

 washing with water. This material can then be used for testing the 

 hydrolytic power of the enzyme on various fats. 



