Differential metabolism of Tyr-MIF-1 and MIF-1 in rat and human plasma.
The metabolism of the endogenous brain peptides Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and MIF-1 (Pro-Leu-Gly-NH2) was determined by HPLC after incubation of the tritiated peptides in human and rat plasma. Degradation of Tyr-MIF-1 was rapid in the plasma from both species, in contrast to the slightly delayed degradation of MIF-1 in rat plasma and the extremely prolonged persistence of MIF-1 in human plasma. In rat plasma, more than half of the intact Tyr-MIF-1 and MIF-1 was degraded within 5 min, in contrast to the 5 days required for 50% degradation of MIF-1 in human plasma at 37 degrees. To slow the rapid rate of metabolism, studies were then performed at 0 degree. Incubation of Tyr-MIF-1 in human plasma at 0 degree for 2 hr resulted in HPLC identification of more Tyr-Pro than Tyr at all times. At 0 degree in rat plasma, however, more Tyr than Tyr-Pro was formed after the first 5 min of incubation of the Tyr-MIF-1 that was labeled on the Tyr. This raised the possibility that the tetrapeptide Tyr-MIF-1 might be serving as a precursor of the tripeptide MIF-1. Incubation of Tyr-MIF-1 tritiated at the Pro under the same conditions with and without Tyr-MIF-1 tritiated at the Tyr showed that Tyr-Pro, not MIF-1, was the predominant degradation product of Tyr-MIF-1. In addition to the metabolism of Tyr-MIF-1 being slower at lower temperatures, it was also slowed by some enzyme inhibitors. After 10 min of incubation at 37 degrees, EDTA appeared to be more effective than bestatin, p-chloromercuribenzoic acid (PCMB), pepstatin, or aprotinin, but after 30 min, bestatin was more effective. Intravenous injection of the tritiated peptides into rats showed short half-time disappearances; again, MIF-1 persisted in blood longer than Tyr-MIF-1. Thus, the results show the rapid metabolism of Tyr-MIF-1 in human and rat plasma, the slightly slower metabolism of MIF-1 in rat plasma, the predominant formation of Tyr-Pro rather than MIF-1 from Tyr-MIF-1, and the markedly delayed metabolism of MIF-1 in human plasma.
Kastin
A J
AJ
VA Medical Center, New Orleans, LA.
Hahn
K
K
Erchegyi
J
J
Zadina
J E
JE
Hackler
L
L
Palmgren
M
M
Banks
W A
WA
D000595:Amino Acid Sequence; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D009075:MSH Release-Inhibiting Hormone / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D008297:Male; D008969:Molecular Sequence Data; D051381:Rats; D013696:Temperature; D013997:Time Factors; D014316:Tritium
D004791:Enzyme Inhibitors; D014316:Tritium; C036930:tyrosyl-prolyl-leucyl-glycinamide; D009075:MSH Release-Inhibiting Hormone