Isolation of stimulatory modulator from rat brain and its specific effect on guanosine 3':5'-monophosphate-dependent protein kinase from cerebellum and other tissues.

Mimicry of selective cytochalasin A (CA) inhibition of cellulase synthesis in the water mold $\text{Achlya}$ by the non-penetrating thiol reagent, p-chloromercuribenzene sulphonate suggests that CA may act as a non-permeant sulphydryl reagent, and that inhibition of cellulase synthesis may be exerted via relatively superficial thiol groups in the plasma membrane.