THF, PMVSIOI.OGV OF 1 1 ,R IILIZATION IN CILIATES 311 



lishcd), and a variety of organic solvents (Mctz, 1946). In spite of 

 these efforts no extract has yet been obtained which inhibits the 

 mating reactivity or otherwise specifically affects animals of com- 

 plementarv mating type. 



Since all attempts at extraction have uniformly met with failure, 

 other methods for characterizing the mating-type substances are re- 

 quired. The most fruitful of these has been a study of the effect of 

 various agents on the mating reactivity of intact paramecia. Of the 

 agents employed (see Table \^), enzymes and "specific group rea- 

 gents" have provided the most positive information regarding the 

 nature of the mating substances. 



Evidently the mating-type substances (P. calk'uisi) are either 

 proteins or substances closely associated with protein, since mating 

 substance activity is destroyed by proteolytic enzymes (Metz and 

 Butterfield, 1951). 



If mating substances are proteins, amino acid residues might 

 well be essential for their activity. To test this possibility certain 

 "protein group reagents" were examined for their effect on mating 

 substance activity. These agents, the conditions under which they 

 were employed, and their effects are given in Table V and discussed 

 below. The various limitations in this type of analysis may be found 

 in several recent works (Glick, 1949; Danielli, 1949, 1953; Barron, 

 1951; Herriott, 1947; Olcott and Fraenkel-Conrat, 1947) and nu- 

 merous short papers. 



Oxidizing and reducing agents do not affect mating reactivity. 

 Likewise, rather drastic treatment with mercuric ion and iodoacetate 

 treatment sufficient to render paramecia nitroprusside negative failed 

 to destroy mating reactivity. Therefore sulfhydryl and disulfide 

 groups are not essential constituents of the mating-type substances 

 (F. calk'msi) . All the amino and phenolic group reagents tested inac- 

 tivated Paramecium when used under the mild conditions generally 

 employed in protein group studies. Therefore it is probable that both 

 of these groups are "essential groups" in the mating-type substances 

 (P. caJkmsi). Thus nitrous acid, dinitrofluorobenzene, and diazonium 

 compounds react with both amino and phenolic groups. Iodine reacts 

 by substitution in phenolic groups (the inactivating action of iodine 

 cannot result from oxidation of sulfhydryl groups since these are not 

 essential), and benzoyl chloride and formalin combine with amino 

 groups. It should be noted that formalin-killed, reactive animals (P. 



