Question

pepsinogen is converted into activity pepsin by

Answer 1

Pepsinogen is a powerful and abundant protein digestive enzyme secreted by the gastric chief cells as a proenzyme and then converted by gastric acid in the gastric lumen to the active enzyme pepsin.

Answer 2

Prepsinogen is a enzyme present in the stomach along with HCl and mucus.  The HCl present in the stomach provides an acidic medium which activates prepsinogen into pepsin so that it can convert big protein molecules into peptites .