Special considerations in the purification of the GM3 ganglioside-forming enzyme, CMP-sialic acid:lactosylceramide alpha 2-3 sialyltransferase (SAT-1): effects of protease inhibitors on rat hepatic SAT-1 activity

Co-purification of an endogenous proteolytic activity has been proposed as the cause for the size heterogeneity of sialyltransferases. Reported herein are results on the effects of various protease inhibitors, sulfhydryl-reducing agents and antimicrobial agents on SAT-1 activity. Addition of protease inhibitors to immunoaffinity-purified rat liver SAT-1 dramatically affects its activity. All protease inhibitors examined, with the exception of PMSF, inhibited the purified enzyme. The most inhibitory were the cysteine (thiol) protease inhibitors. This effect is less spectacular when the effect of these inhibitors was studied on SAT-1 activity in Golgi-enriched microsomes, although the inhibition was greatest by the cysteine protease inhibitors. One dramatic effect, found in both cases, was the apparent activation of SAT-1 activity in the presence of beta-mercaptoethanol.