ABSTRACT
Figure 20. 2 Functio n o f ubiquit i n i n extralysosoma l protei n degradation . U b i s ubi - quit in; E l x E 2 , and E 3 are activatin g enzymes; CF 2 , CF 2 , and CF 3 are degradatio n enzymes . (Reproduced w i t h permissio n from Hershk o A. Ubiquitin-mediated protei n degradation . J Biol Chem 263:15237-15240 , 1989. )
The nonlysosoma l degradatio n o f protein s i s rapi d an d apparentl y unaf -
fected b y hormones . A majo r system involve s a small-molecular-weigh t protei n
called ubiquitin , w h i c h combine s wi t h th e protei n t o b e degrade d an d make s i t
susceptible t o proteolytic attack . This combination involves th e carboxyl groups o f
ubiquitin and the N-termina l groups o f proteins. A T P i s required for this reaction.
