A monoclonal antibody to the phosphorylated form of phenylalanine hydroxylase. Definition of the phosphopeptide epitope.

Monoclonal antibody PH7 has specificity for the phosphorylated form of the human liver phenylalanine hydroxylase and negligible reactivity towards the dephosphorylated form of the native enzyme by enzyme-linked immunoassay. PH7 binds specifically to the phosphorylated form of the liver enzyme after SDS/polyacrylamide-gel electrophoresis and transfer to nitrocellulose. Competitive blocking assays have been applied in conjunction with reversed-phase h.p.l.c. of purified tryptic fragments of human liver phenylalanine hydroxylase to localize the epitope. The major immunoreactive tryptic peptide cross-reacting with PH7 had an amino acid analysis corresponding to the first 41 amino acids of the human liver phenylalanine hydroxylase sequence and included the serine residue that is thought to be the phosphorylation site. The monoclonal antibody recognized the phosphorylated form of the synthetic decapeptide corresponding to the local phosphorylation-site sequence Gly-Leu-Gly-Arg-Lys-Leu-Ser(P)-Asp-Phe-Gly, but not the dephosphodecapeptide. Thermolysin digestion of the peptide demonstrated the monoclonal antibody bound to the pentapeptide Leu-Ser(P)-Asp-Phe-Gly. Monoclonal antibody PH7 recognized the phosphodecapeptide at concentrations 10(3)-fold higher than with phenylalanine hydroxylase, compared with 10(4)-10(7)-fold higher for other phosphopeptides and phosphoproteins. The results demonstrate that monoclonal antibody PH7 has specificity for the phosphorylated form of phenylalanine hydroxylase at the phosphorylation site.

Derivation of neutralizing monoclonal antibodies to human rotaviruses and evidence that an immunodominant neutralization site is shared between serotypes 1 and 3.

Neutralizing monoclonal antibodies were derived to human rotaviruses RV-4 (serotype 1), RV-5 (serotype 2), and ST-3 (serotype 4). By enzyme immunoassay and fluorescent focus neutralization, eight of the antibodies appeared to be specific for the immunizing serotype, and so have potential as reagents for rotavirus serotyping by enzyme immunoassay. Seven of these were shown by Western blotting, enzyme immunoassay for antibody additivity, and reaction with rotavirus reassortants, to be directed against the major outer capsid glycoprotein. The remaining serotype-specific antibody immunoprecipitated the 84-kD outer capsid protein. One antibody reacted with all serotype 1 and 3 rotaviruses but not with serotypes 2 or 4. When tested with virus mutants, this antibody recognized an immunodominant determinant of neutralization shared between serotypes 1 and 3 on the major outer shell glycoprotein. Our results suggest that two outer capsid proteins possess determinants of neutralization, and that viruses of different serotypes may share immunodominant neutralization sites.

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

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 (Mr = 50,000) and L (Mr = 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 [gamma-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 serine 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.