Catalytic unit-independent phosphorylation and dephosphorylation of type II regulatory subunit of cyclic AMP-dependent protein kinase in rat liver plasma membranes

Endogenous phosphorylation and dephosphorylation of rat liver plasma membrane proteins, suggesting a 18 kDa phosphoprotein as a potential substrate for alkaline phosphatase

Purified rat liver plasma membranes were incubated for 0-60 min with [gamma-32P]ATP and analysis of 32P-labeled proteins by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed the presence of two shifted kinetic phenomena. The use of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), a potent inhibitor of protein kinases, allowed the identification of one as the endogenous protein phosphorylation. The other was shown to be the labeling of two phospho-intermediate forms of alkaline phosphatase (orthophosphoric monoester phosphohydrolase (alkaline optimum, EC 3.1.3.1.], which have apparent molecular masses of 151 and 135 kDa. Bromolevamisole, a potent inhibitor of the enzyme, stabilized these phospho-intermediates, and consequent on this inhibition the labelling of a 18 kDa phosphoprotein was augmented. So, when alkaline phosphatase was studied in its native plasma membrane environment, a specificity of this enzyme over the endogenous phosphoproteins was established.

Identification of a 50-kDa Ca-, cAMP-, and cGMP-dependent epithelial phosphoprotein as a cAMP regulatory protein

Multiple second messengers, presumably acting via protein phosphorylation mechanisms, regulate flounder intestinal ion transport. We recently reported [C. Toskulkao, N. T. Nash, K. Leach, and M. C. Rao. Am. J. Physiol. 258 (Cell Physiol. 27): C879-C888, 1990] that this tissue possesses adenosine 3',5'-cyclic monophosphate (cAMP)- and guanosine 3',5'-cyclic monophosphate (cGMP)-specific protein kinases, types II and III Ca-calmodulin kinases, and very low levels of protein kinase C. These results correlate with ion transport studies in which cGMP and Ca were shown to inhibit salt absorption, cAMP to increase anion permeability, and phorbol esters to have no effect. In the present study we characterized in detail a 50-kDa protein the phosphorylation of which is regulated by more than one second messenger. The 50-kDa (pI 5.2) phosphoprotein is present in both the cytosol (50 kDa-C) and particulate (50 kDa-P) fractions and appears to be regulated by Ca, cAMP, and cGMP. Although the pI and Mr of the regulated proteins are identical, there are differences in the regulation of 50 kDa-P and 50 kDa-C. The phosphorylation of 50 kDa-P is high in the basal state, and Ca and cGMP enhance this. cAMP has a biphasic effect, increasing it at low and decreasing it at high protein concentrations. The isoquinoline derivatives H-8 [50% effective dose (ED50) approximately 2.3 microM] and H-7 (ED50 approximately 45 microM) inhibit basal 50 kDa-P phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of parathion and methylparathion on protein content of chicken embryo muscle in vivo

Chicken eggs were treated with 0.4 per cent solutions of parathion or methylparathion for four or eight days, and the two-dimensional gel electrophoretic protein pattern of cervical muscles of eighteen days old embryos was analyzed. Both compounds significantly decreased the content of alpha-actinin, alpha-tubulin and beta-tubulin after four days treatment, and, in addition, that of three other related proteins (gamma-proteins) after eight days treatment. Under in vitro phosphorylating conditions, both methylparathion and parathion specifically inhibited the phosphorylation of one isoform of beta-tubulin. Data suggest that the muscle-damaging effects of organophosphorous insecticides, such as parathion and its derivates, may be related to the decrease of tissue content of certain cytoskeletal proteins.

The cAMP cascade in the nervous system: molecular sites of action and possible relevance to neuronal plasticity

Many intercellular messages regulate the activity of their target cells by altering the intracellular level of cAMP and, as a consequence, the phosphorylation state of proteins which serve as substrates for cAMP-dependent protein kinase. Such regulation plays a crucial role in neuronal development, neuronal function, and neuronal plasticity (e.g., elementary learning mechanisms). Ample information has been accumulated in recent years on the enzymes that regulate the level of cAMP or respond to it, on the regulation of cAMP synthesis by neurohormones, neurotransmitters, ions, and toxins, on neuronal-specific substrate proteins that are phosphorylated by the cAMP-dependent kinase, and on the interaction of the cAMP-cascade with other second-messenger systems within neurons. Such data, obtained by a combination of molecular-biological, biochemical, and cellular approaches, shed light on the detailed mechanisms by which modulation of a ubiquitous molecular cascade leads to a great variety of short-term as well as long-term specific neuronal responses and alterations.

Phorbol ester and 1,2-diolein are not fully equivalent activators of protein kinase C in respect to phosphorylation of membrane proteins in vitro

Phosphorylation of liver plasma proteins by protein kinase C was studied by using the two best known activators of the enzyme, 12-O-tetradecanoylphorbol-13-acetate (TPA) and 1,2-diolein. While the effects of TPA and diolein were almost identical on two proteins and similar in magnitude on four proteins, the phosphorylation of an additional four proteins was increased only by TPA. We conclude that in respect to phosphorylation of membrane proteins, TPA and diglycerides are not fully equivalent activators of kinase C.