α-Branched 1,2-Diacyl Phosphatidylcholines as Effectors of Activity of Cytochrome P450SCC (CYP11A1)

Abstract

We synthesized phosphatidylcholines with fully saturated branched fatty acyl chains substituted in the 2-positions of the main chains and studied the influence of these lipids on the activity and other properties of P450SCC in vesicle-reconstituted systems. These saturated branched lipids, with regard to the fatty acyl moiety in molecular shape similar to cardiolipin but with the headgroup of phosphatidylcholines retained, showed a stimulatory efficiency higher than any other phospholipid and at least comparable to cardiolipin. Activation is sensitive to the acyl chain structure and composition. Results suggest that the shape of the molecule at least partially plays an important role in the process of stimulation of the activity of P450SCC. Because binding of cholesterol was increased by the branched lipids monitored optically by the fraction of P450SCC in the high spin form, it was concluded that these lipids, like cardiolipin and other lipids, exert their effects by regulating the binding of cholesterol to P450SCC. These data suggest that polymorphic lipids such as branched phosphatidylcholines and cardiolipin might influence P450SCC function by maintenance of the membrane curvature at a value optimal for activity.

Branched Phosphatidylcholines Stimulate Activity of Cytochrome P450SCC (CYP11A1) in Phospholipid Vesicles by Enhancing Cholesterol Binding, Membrane Incorporation, and Protein Exchange

“…nary results obtained in DOPC vesicle systems suggested that the stimulation of P450SCC activity by branched PCs is correlated with the fraction of the enzyme in the high spin form (8) as has been discussed earlier for CL and other activator lipids (5-7). The complexation of CHL with P450SCC causes a conversion of heme iron from the low spin to the high spin form, which can be monitored in the Soret region of the absorption spectrum (17,6).…”

“…To facilitate direct comparison of the results with previ-ous data, values were normalized to 100% maximum activity. The 100% value correspond to 5.8, 6.0, 6.5, 4.6, 5.3 nmol pregnenolone/min/nmol P450SCC for DMPC/PC(10,6), DMPC/ PC (12,8), DMPC/PC(14,10), DMPC/CL, and DOPC/PC(14,10), respectively. In DMPC vesicles, the rate of pregnenolone formation increases with the proportion of PC(14,10) from a turnover number of 0.45 min Ϫ1 in the absence of PC(14,10) to 6.5 min Ϫ1 with 47 mol % PC (14,10).…”

“…It has been recently reported by us that certain branched PCs that in the structure of their hydrophobic part are similar to CL but have fully saturated acyl chains cause potent activation of P450SCC comparable only with those by CL (8). By systematic variation of the lengths of both the branched and main chains of these lipids and systematic introduction of unsaturation, we found a relationship between the potency of activation of these PCs and their capacity to increase the propensity of the membrane to form nonbilayer phases.…”

“…It has been shown for CL and other activator lipids that their influence is realized via binding to P450SCC followed by an increase of CHL binding to the enzyme (5)(6)(7). Based on preliminary optical measurements in DOPC vesicles, we have suggested (8) that the presence of the branched PCs is related to a significant enhanced content of the high spin form of P450SCC, which is connected with a higher portion of P450SCC to be complexed with its substrate CHL, too. In addition, there are other properties of P450SCC in reconstituted systems that may be affected by branched PCs and lead to subsequent activity increase, e.g.…”

How did cells get their size?

“…activity depends on vesicle size in a manner related to membrane curvature (Madden et al, 1984;Schwarz et al, 1996). Respiration in mitochondria and photosynthesis in chloroplasts vary with osmotic membrane stretch (Mathai et al, 1993), and chloroplast membranes exhibit MS ion fluxes (Kikuyama and Tazawa, 2001) and swelling sensitive rates of photosynthesis (Paillotin et al, 1998).…”