Oxidized forms of parathyroid hormone with biological activity. Separation and characterization of hormone forms oxidized at methionine 8 and methionine 18.

Bovine parathyroid hormone (PTH) was oxidized with hydrogen peroxide, and the oxidation products were separated by reverse phase high performance liquid chromatography. Using a shallow gradient, four major peaks (peaks I-IV in order of elution) were identified and completely separated from one another. Peak IV co-eluted with fully reduced PTH. The earliest eluting peak (peak I) could be reduced with mercaptoethylamine to produce all three of the later eluting ones. The second peak could be reduced back to peak IV but not to peak III, while peak III could be oxidized to peak I but not to peak II. These data plus the kinetics of oxidation showed that peaks II and III are intermediate in the generation of I from IV or IV from I, but were not generated from one another. Amino acid analysis showed that peak I contains no methionine and two residues of methionine sulfoxide, peaks II and III one methionine sulfoxide each, and peak IV two residues of methionine and no sulfoxide. Study of the peptides produced from each form of PTH by cleavage with cyanogen bromide showed that peak II is oxidized at methionine 8 and peak III at methionine 18 while peak I is oxidized at both methionines. The biological activity of each peak was determined in the kidney membrane adenylyl cyclase assay. All forms were active but with widely varying potencies (peak IV greater than peak III greater than peak II greater than peak I).