Bony Targets of Non-"skeletal" Hormones 



219 



gradient; 2) pinocytosis — the name currently given to the active engulfing of 

 materials by cells through invaginations of the plasma membrane; and 3) the pro- 

 cesses of transport under which name all cell membrane transfer systems involving the 

 concept of a carrier have been grouped. 



Possible modes ofocfion of hormones at the molecular level 



On a membrane 

 -OifTusion (integrity) 



■■■■Pinocytosis 



energy substrate 

 ai^o/Mtity 



—■Transport 



active or "facilitated" 



^ Kr. ^ 



availabiiity ovaitoMity 



energy carrkr^^ qq^^ 



Biosynthesis bindim Destruction 

 Competitive Non-competitive 



_^ On a enzyme 



—Activity 



Inhibition Acl 



y ^ - . „ 



'ive Non-competitive Degradation t 



vtivotion 



■Availability 



vsis fe lease Destruction 

 from 

 membrane 

 —■Environment 



pW Ions H^O 



On transfer of genetic information 

 ■■■■fronslationofDNA "message" 



■■■■ "Messenger'RNA 

 Biosynthesis Release Destruction 



The rate of transfer of a substance by any of these methods depends on a variety 

 of factors potentially amenable to modification by hormones. Even the rate of 

 transfer by diffusion (the simplest case) depends on pore size, charge, bound ions etc. 

 while the 2 more complex processes are often coupled to cell metabolic activity and 

 potentially depend on a host of items. Thus pinocytosis, which clearly involves cell 

 movement and new membrane synthesis, must depend at least on the availability of 

 pools of energy and appropriate substrate. In the case of transport, besides energy to 

 drive the system, a carrier must be supplied whose movement in the membrane (real 

 or apparent) depends on some of the same factors as diffusion. The availability of 

 this carrier to transport a given molecular species will, in turn, depend on its rate of 

 biosynthesis, its rate of destruction, and the degree to which it is bound — either to 

 the material under study or some competitive molecule. While this analysis obviously 

 could be carried further enough has been said to indicate the general line of reasoning 

 which can be pursued. 



Clearly, the processes of transport, pinocytosis and even diffusion must ultimately 

 depend on enzymes and their activity. Thus potential effects of hormones on enzymes 

 form the second major area which must be considered in any survey of molecular 

 mechanisms which might be affected by these substances. 



A direct effect of a hormone on an enzyme or enzyme system could occur in 

 3 ways: through direct modification of its action on its substrate, through changes in 

 the total quantity of enzyme available, or through changes in the local environment 

 in which it has to act. As in the case of potential effects on membrane transfer 

 systems, possible modes of action each worthy of investigation are suggested for each 

 category by current knowledge. It is noteworthy that when these are examined the 

 only wholly novel possible actions which present themselves in this area are those 



