Rat progastrin processing yields peptides with altered potency at the CCK-B receptor.
Details of prohormone processing patterns are revealed by purification and characterization of molecular forms stored in the tissues where the hormones are expressed. Molecular forms of rat gastrin were purified from antral extracts by gel permeation, anion exchange, and reverse-phase HPLC. Amidated and glycine-extended gastrins were detected with specific antisera and their structures determined by mass spectrometry. In rats, the only form shorter than gastrin-17 observed contained 16 amino acids. These data suggest that two enzymes process the amino terminus of gastrin-17. Pyrrolidone carboxylic acid peptidase removes the amino terminal pyrrolidone carboxylic acid (pyroGlu), forming gastrin-16. In mammals other than rat, gastrin-16 is then cleaved by dipeptidyl peptidase IV to form gastrin-14. In rat, this reaction does not take place because of proline residues Pro(2)-Pro(3)- in gastrin-16. Gastrin-16 is found in sulfated and nonsulfated forms and comprises 28% of the total gastrin immunoreactivity. Glycine-extended forms of gastrin-16 and gastrin-17 comprises 45% of the total gastrin immunoreactivity. The sulfated forms of gastrin-16 and gastrin-17 bind to the CCK-B receptor transfected into CHO cells with 10-fold higher affinity than the nonsulfated forms of these peptides. Therefore, processing of rat progastrin may modulate the expression of gastrin biological activity.
Keire
David A
DA
CURE/UCLA Digestive Disease Research Center, West Los Angeles Veterans Administration Medical Center, Building 115, Room 117B, 11301 Wilshire Blvd, Los Angeles, CA 90073, USA.
Vincent Wu
S
S
Diehl
David L
DL
Chew
Peter
P
Ho
Fang-Jen
FJ
Davis
Michael T
MT
Lee
Terry D
TD
Shively
John E
JE
Walsh
John H
JH
Reeve
Joseph R
JR
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002850:Chromatography, Gel / Q000379:methods; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange / Q000379:methods; D006224:Cricetinae; D005755:Gastrins / Q000378:metabolism*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051381:Rats; D043887:Receptor, Cholecystokinin B / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
D005755:Gastrins; D010455:Peptides; D011498:Protein Precursors; D043887:Receptor, Cholecystokinin B