Regulation of the plasma membrane type III phosphatidylinositol 4-kinase by positively charged compounds.
The effects of positively charged compounds on a plasma membrane, type III phosphatidylinositol 4-kinase were studied. To determine whether the enzyme would respond differently to the compounds in a membrane-associated versus a soluble state, both the plasma membrane and solubilized (released by 0.01% (v/v) Triton X-100) PI 4-kinase were used. Spermidine, spermine, polylysine, cardiotoxin, melittin, and histone stimulated the solubilized PI 4-kinase but had little effect on or weakly stimulated the membrane-associated PI 4-kinase. Polyarginine inhibited membrane-associated PI 4-kinase 75% and inhibited the solubilized PI 4-kinase 30%, indicating that charge alone was not sufficient for activation. Polyarginine also eliminated the activation of the solubilized PI 4-kinase by a PI 4-kinase activator protein, PIK-A49. Calmodulin, a common calcium-binding protein, at micromolar levels strongly inhibited solubilized PI 4-kinase activity but did not inhibit membrane-associated PI 4-kinase activity. The inhibition of the solubilized PI 4-kinase by calmodulin was calcium independent. Calcium alone (1 microM-0.1 mM) inhibited PI 4-kinase activity only slightly (< 30%). The differential effects of the positively charged compounds on the solubilized and membrane-associated PI 4-kinase were not due to substrate availability because both enzymes were assayed in the presence of excess PI (0.6 mM) and 0.3% (v/v) Triton X-100. The data suggest that positively charged compounds affected the enzyme activity not only by interacting with the substrates or products of the reaction but also by interacting with the PI 4-kinase or regulatory components in the plasma membrane.
Yang
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W
Botany Department, North Carolina State University, Raleigh 27695-7612.
Boss
W F
WF
D019870:1-Phosphatidylinositol 4-Kinase; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology; D002412:Cations; D002462:Cell Membrane / Q000201:enzymology; D004179:Cobra Cardiotoxin Proteins / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006657:Histones / Q000494:pharmacology; D066298:In Vitro Techniques; D008555:Melitten / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011073:Polyamines / Q000494:pharmacology; D011107:Polylysine / Q000494:pharmacology; D014675:Vegetables
D002147:Calmodulin; D002412:Cations; D004179:Cobra Cardiotoxin Proteins; D006657:Histones; D010455:Peptides; D011073:Polyamines; D008555:Melitten; D011107:Polylysine; C015462:polyarginine; D017853:Phosphotransferases (Alcohol Group Acceptor); D019870:1-Phosphatidylinositol 4-Kinase; D002118:Calcium