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Enzymatic methyl esterification of pituitary polypeptides.
International Journal of Peptide and Protein Research
|March 1, 1979
Summary
Protein methylase II methylates pituitary polypeptides like lutropin and adrenocorticotropin. Specific subunits and fragments show varying methyl-accepting activity, with some fragments regaining activity upon preincubation.
Area of Science:
- Biochemistry
- Molecular Biology
- Endocrinology
Background:
- Protein methylation is a crucial post-translational modification.
- Protein methylase II (PM-II) catalyzes the methyl esterification of protein carboxyl groups.
- Pituitary polypeptides play vital roles in endocrine regulation.
Purpose of the Study:
- To investigate the methyl esterification of pituitary polypeptides by PM-II.
- To identify which pituitary polypeptides and their fragments serve as substrates for PM-II.
- To characterize the kinetics of this enzymatic reaction.
Main Methods:
- Enzymatic assays using purified protein methylase II.
- Incubation of ovine lutropin, adrenocorticotropin (ACTH), and beta-lipotropin with PM-II.
- Analysis of methyl esterification in intact proteins and their fragments.
- Kinetic studies of substrate methylation.
Main Results:
- Ovine lutropin and alpha1-39-ACTH were identified as efficient methyl acceptor substrates.
- Beta-lipotropin showed moderate methyl-accepting activity.
- The alpha-subunit of lutropin was active, while the beta-subunit was inactive.
- Specific fragments of ACTH (alpha7-38-ACTH and alpha1-17-ACTH) exhibited differential methyl-accepting capacities, with combined fragments restoring full activity.
Conclusions:
- Protein methylase II efficiently methylates specific pituitary polypeptides.
- Substrate recognition and activity are dependent on the polypeptide's primary structure and specific domains.
- The study provides insights into the enzymatic modification of key endocrine hormones.