In vitro metabolic degradation of a bovine growth hormone-releasing factor analog Leu27-bGRF(1-29)NH2 in bovine and porcine plasma. Correlation with plasma dipeptidylpeptidase activity.
A bovine growth hormone-releasing factor analog, Leu27-bGRF(1-29)NH2, was rapidly hydrolyzed to Leu27-bGRF(3-29)NH2 when incubated at 0.03 mM with porcine and bovine plasma at 37 degrees C in vitro (t1/2 = 8.4 min and 22.1 min, respectively). The site of cleavage was the same as that reported by Frohman et al. (J. Clin. Invest. 78, 906-913, 1986) for the GRF/human plasma system and was suggested by the authors to be due to the presence of dipeptidylpeptidase IV (DPP-IV) in human plasma. The DPP-IV-like activity of porcine plasma, determined with Gly-Pro-p-nitroanilide as substrate at pH 7.6 was about 2- to 3-fold higher than that of bovine plasma and seems to correlate well with the more rapid degradation of the GRF analog in porcine plasma. The hormone half-life was extended to 83.3 min when Leu27-bGRF(1-29)NH2 was incubated in vitro with bovine plasma in the presence of an equimolar amount of diprotin A (a competitive DPP-IV inhibitor). Dipeptidylpeptidase II-like activity of porcine and bovine plasma (which may overlap with substrate specificity of DPP-IV) was measured with Lys-Ala-beta-naphthylamide and at pH 7.6 was found to be relatively low (3% and 21% of the corresponding plasma DPP-IV activities). Tyr-beta-naphthylamide was hydrolyzed slowly by porcine plasma and not degraded at all by bovine plasma, which suggests that the sequential cleavage from the GRF N-terminus starting with Tyr at position 1 is not dominant.(ABSTRACT TRUNCATED AT 250 WORDS)
Kubiak
T M
TM
Division of Reproduction and Growth Physiology, Upjohn Company, Kalamazoo, MI 49001.
Kelly
C R
CR
Krabill
L F
LF
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone / Q000097:blood / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D013058:Mass Spectrometry; D010446:Peptide Fragments / Q000097:blood / Q000378:metabolism*; D017337:Sermorelin / Q000031:analogs & derivatives*; D013552:Swine
D000596:Amino Acids; D010446:Peptide Fragments; C061235:somatotropin releasing hormone (1-29) amide, 27-Leu-; D017337:Sermorelin; D013007:Growth Hormone-Releasing Hormone; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases