Differential hydrolysis of bovine parathyroid hormone and its N-terminal peptide by rat kidney.

Highly purified bovine parathyroid hormone (b-PTH 1-84) and its synthetic N-terminal peptide (b-PTH 1-34) were labelled with 125-I and incubated with rat kidney homogenate at 37 degrees C for 1 hour to assess the degree of hydrolysis of the iodinated peptides through measurement of the increase of trichloroacetic acid soluble 125-I fraction. Rat kidney homogenate rapidly hydrolyzed b-PTH 1-84 but was scarcely effective in hydrolyzing b-PTH 1-34. When 125-I labelled b-PTH 1-84 and b-PTH 1-34 were injected intravenously in rats, hydrolysis in vivo of the former appeared to be much more rapid than that of the latter, as shown by the faster disappearance from plasma of trichloroacetic acid precipitable fraction. Incubation of b-PTH (1-84) with rat kidney homogenate caused a shift of 125-I PTH peak almost to the position of salt peak, while the position of 125-I b-PTH (1-34) was almost unchanged by incubation with rat kidney homogenate. N-terminal peptide of bovine parathyroid hormone thus appears to be less susceptible to hydrolytic degradation by rat tissue than the intact hormone, with resultant longer retention in the blood stream.