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Two apparent molecular weight forms of human and monkey phenylalanine hydroxylase are due to phosphorylation

journal contribution
posted on 2023-02-06, 22:50 authored by SC Smith, BE Kemp, WJ McAdam, Julian MercerJulian Mercer, RG Cotton
Two-dimensional polyacrylamide gel analyses of purified human and monkey liver phenylalanine hydroxylase reveal that the enzyme consists of two different apparent molecular weight forms of polypeptide, designated H (M(r) = 50,000) and L (M(r) = 49,000), each containing three isoelectric forms. The two apparent molecular weight forms, H and L, represent the phosphorylated and dephosphorylated forms of phenylalanine hydroxylase, respectively. After incubation of purified human and monkey liver enzyme with purified cAMP-dependent protein kinase and [γ-32P]ATP, only the H forms contained 32P. Treatment with alkaline phosphatase converted the phenylalanine hydroxylase H forms to the L forms. The L forms but not the H forms could be phosphorylated on nitrocellulose paper after electrophoretic transfer from two-dimensional gels. Phosphorylation and dephosphorylation of human liver phenylalanine hydroxylase is not accompanied by significant changes in tetrahydrobiopterin-dependent enzyme activity. Peptide mapping and acid hydrolysis confirm that the apparent molecular weight heterogeneity (and charge shift to a more acidic pI) in human and monkey liver enzyme results from phosphorylation of a single serin residue. However, phosphorylation by the catalytic subunit of cAMP-dependent protein kinase does not account for the multiple charge heterogeneity of human and monkey liver phenylalanine hydroxylase.

History

Journal

Journal of Biological Chemistry

Volume

259

Pagination

11284-11289

Location

United States

ISSN

0021-9258

eISSN

1083-351X

Language

English

Issue

18

Publisher

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC