OXIDASES 273 



invariable accompaniment of the activity of the clotting enzymes, 

 although no actual connection of its presence with the chemical 

 changes has been demonstrated. 



Rennet is found in the seeds and fruits of a number of plants, 

 and is also present in some bacteria. It is capable of acting in 

 acid, neutral or alkaline solutions. 



350, Pectase. Pectase is almost universally distributed in 

 plants and is most abundant in the growing regions. Certain 

 changes which take place in the cell-membranes during the life 

 of the protoplast are supposed to be due to its action. The cellu- 

 lose of the wall is accompanied by the presence of other sub- 

 stances among which are pectine and pectic acid, which may be 

 derived from pectose. Pectine is most abundant in the mem- 

 branes of younger cells, and compounds of pectic acid increase in 

 abundance with age ; this action however, ensues only before the 

 beginning of suberization and lignification. 



The middle lamella of cell-membranes has long been known to 

 differ chemically from the layers contiguous to the ectoplasm, 

 and the hypothesis has been advanced that the action of pectase 

 converts pectine into pectic acid, which slowly passes outwardly 

 through the wall from each protoplast by exudation pressure, and 

 combines with calcium salts to form calcic pectate, which is depos- 

 ited on the external surface of the wall. At points in which the 

 walls of contiguous cells are in contact a layer of calcic pectate 

 formed from contributions from both cells would be laid down as 

 the middle lamella. A free layer of the substance would result 

 where the cell abuts on an intercellular space. This theory is 

 supported substantially by the fact that the middle lamella may 

 be dissolved by the reagents in which calcic pectate is known to 

 be soluble. 



351. Oxidases. The oxidases include a number of enzymes 

 which have the power of producing oxidation in various com- 

 pounds including fatty acids and sugars. Although no actual 

 demonstration has been made, it is supposed in some cases that 

 the energy liberated in the process becomes available to the pro- 



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