Abstract:
:CaATPase from rabbit sarcoplasmic reticulum (SR) has been isolated, purified, and reconstituted into unilamellar vesicles with 1,2-dipentadecanoylphosphatidylcholine (DPePC) and acyl-chain-perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC-d62). For total lipid:protein mole ratios between 25 and 70, a constant "hard-to-exchange" phospholipid population (HEPP) of 12 +/- 4 native phospholipid molecules per protein monomer is observed, consistent with the studies of Bick et al. [(1991) Arch. Biochem. Biophs. 286, 346-352]. Thermotropic and conformational properties of the lipids in native SR and in the reconstituted systems were probed with FT-IR spectroscopy. The native SR phospholipids undergo a broad phase transition centered at about 1-2 degrees C and are thus disordered under physiological conditions. The thermotropic behavior of CH2 wagging progressions characteristic of the palmitate chains differs from that of the total lipid population and is suggestive of membrane microheterogeneity. The individual thermotropic and conformational properties of the HEPP and the exogenous lipid in reconstituted vesicles containing CaATPase and DPPC-d62 were monitored. At temperatures below the onset of the gel-liquid-crystal phase transition, the HEPP possesses significant conformational disorder, and exhibits the monotonic introduction of gauche rotamers as the temperature is raised from -55 to 27 degrees C, in contrast to the exogenous lipid, which exhibits a constant high order over the same temperature range. Nevertheless, the HEPP undergoes a residual order-disorder phase transition with similar but not identical parameters (half-width, midpoint temperature) to the gel-liquid-crystal transition of the bulk (exogenous) lipid in the reconstituted systems.(ABSTRACT TRUNCATED AT 250 WORDS)
journal_name
Biochemistryjournal_title
Biochemistryauthors
Senak L,Mendelsohn Rdoi
10.1021/bi00075a024subject
Has Abstractpub_date
1993-06-22 00:00:00pages
6288-94issue
24eissn
0006-2960issn
1520-4995journal_volume
32pub_type
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