Phosphorylation of type‐L pyruvate kinase in intact hepatocytes Localisation of the phosphorylation site in response to both glucagon and the Ca²⁺‐linked agonist phenylephrine

Abstract

Pyruvate kinase is one of the enzymes which can be phosphorylated by stimulation of the cell with either glucagon or Ca 2 ÷-linked hormones. Whether these two classes of hormones phosphorylate the same site on the enzyme is unclear. Our results demonstrate that isolation of [32p]phosphorylated type-L pyruvate kinase from glucagon-treated hepatocytes followed by aspartyl-prolyl cleavage yields a [32p]phosphorylated peptide of Mr 17000. This fragment is also phosphorylated in response to the Ca2+-mediated agonist phenylephrine.

Modification of pyruvate kinase and lactate dehydrogenase in foot muscle of the sea mussel Mytilus galloprovincialis under anaerobiosis and recovery

“…This mechanism of PK modification was found to be due to the effect of environmental hypoxia on the organism of the mollusc Patella caerulea (15), the worm Phascolosoma arcuatum (16), and the land snail Otala lactea (17). Although muscle PK is not a regulatory enzyme in vertebrates (18), in invertebrates this enzyme is regulatory and is analogous to its liver form from vertebrates (3)(4)(5)(15)(16)(17).…”

Insulin regulation of pyruvate kinase activity in cultured rat hepatocytes, in the presence of vasopressin, ionophore A23187 or 4β-phorbol 12β-myristate 13α-acetate

“…Phenylephrine and vasopressin inhibit PK activity (Chan & Exton, 1978;Claus et al, 1979;Garrison et al, 1979;Blair et al, 1979;Staddon & Hansford, 1987) and phosphorylate the enzyme (Garrison et al, 1979(Garrison et al, , 1984Garrison & Wagner, 1982;Knowles & Hems, 1983;Hsu et al, 1987). Direct phosphorylation of PK by Ca2l/ calmodulin-dependent protein kinase has been demonstrated at a serine residue that is also phosphorylated by the cyclic-AMP-dependent protein kinase (Schworer et al, 1985) as well as a threonine residue that is five residues from the serine (Soderling et al, 1986).…”