Proteolytic modification of growth hormone by a rat kidney lysosomal protease.

A protease activity has been detected in rat kidney which has some degree of specificity to cleave native bovine growth hormone (bGH). The enzyme has an optimum pH of about 5.0, is dependent on thiol reagents and non-inhibited by EDTA or Aprotinin. Controlled digestion of bGH leads to a derivative retaining growth promoting activity, while showing a different physicochemical behavior from that of the native hormone. The data support the hypothesis of the kidney, among other tissues, originating active forms of growth hormones.