Influence of the physical state of the membrane on the enzymatic activity and energy of activation of protein kinase C alpha.
The activation of protein kinase C alpha was studied by using a lipid system consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS) (molar ratio 4:1) and different proportions of 1-palmitoyl-2-oleoyl-sn-glycerol (POG). The phase behavior of the lipidic system was characterized by using differential scanning calorimetry and 31P NMR, and a phase diagram was elaborated. The results suggested the formation of two diacylglycerol/phospholipid complexes, one at 15 mol % of POG and the second at 30 mol % of POG. These two complexes would define the three regions of the phase diagram: in the first region (concentrations of POG lower than 15 mol %) there is gel-gel immiscibility at temperatures below that of the phase transition between C1 and pure phospholipid, and a fluid lamellar phase above of the phase transition. In the second region (between 15 and 30 mol % of POG), gel-gel immiscibility between C1 and C2 with fluid-fluid immiscibility was observed, while inverted hexagonal HII and isotropic phases were detected by 31P NMR. In the third region (concentrations of POG higher than 30 mol %), gel-gel immiscibility seemed to occur between C2 and pure POG along with fluid-fluid immiscibility, while an isotropic phase was detected by 31P NMR. When PKC alpha activity was measured, as a function of POG concentration, maximum activity was found at POG concentrations as low as 5-10 mol %; the activity slightly decreased as POG concentration was increased to 45 mol % at 32 degrees C (above Tc) whereas activity did not change with increasing concentrations of POG at 5 degrees C (below Tc). When the activity was studied as a function of temperature, at different POG concentrations, and depicted as Arrhenius plots, it was found that the activity increased with increasing temperatures, showing a discontinuity at a temperature very close to the phase transition of the system and a lower activation energy at the upper slope of the graph, indicating that the physical state of the membrane affected the interaction of PKC alpha with the membrane.
Jiménez-Monreal
A M
AM
Departamento de Bioquímica y Biología Molecular "A", Facultad de Veterinaria, Universidad de Murcia, Spain.
Aranda
F J
FJ
Micol
V
V
Sánchez-Piñera
P
P
de Godos
A
A
Gómez-Fernández
J C
JC
D000818:Animals; D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004075:Diglycerides / Q000737:chemistry; D004734:Energy Metabolism; D004789:Enzyme Activation; D007527:Isoenzymes / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010713:Phosphatidylcholines / Q000737:chemistry; D010718:Phosphatidylserines / Q000737:chemistry; D011493:Protein Kinase C / Q000737:chemistry*; D051571:Protein Kinase C-alpha; D013552:Swine; D013696:Temperature
D004075:Diglycerides; D007527:Isoenzymes; D008563:Membrane Lipids; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; C034973:1-oleoyl-2-palmitoylphosphatidylcholine; C083975:1-palmitoyl-2-oleoyl-sn-glycerol; C050294:1-palmitoyl-2-oleoylglycero-3-phosphoserine; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha