title: Identification and Partial Characterization of the Denaturation Transition of the Light Harvesting Complex II of Spinach Chloroplast Membranes.
abstract: Differential scanning calorimetry was employed to investigate the structure of spinach (Spinacia oleracea) chloroplast membranes. In a low ionic strength Hepes-buffered medium, major calorimetric transitions were resolved at 42.5 degrees C. (A), 60.6 degrees C (B), 64.9 degrees C (C(1)), 69.6 degrees C (C(2)), 75.8 degrees C (D), 84.3 degrees C (E), and 88.9 degrees C (F). A lipid melting transition was also commonly seen at 17 degrees C in scans starting at lower temperatures. The D transition was demonstrated by four independent methods to derive from denaturation of the light harvesting complex associated with photosystem II (LHC-II). Evidence for this conclusion was as follows: (a) the endotherm of the isolated LHC-II (74.0 degrees C) was very similar to that of D (75.8 degrees C); (b) the denaturation temperature of the 27 kilodalton LHC-II polypeptide determined in intact chloroplast membranes by thermal gel analysis was identical to the temperature of the D transition at pH 7.6 and after destabilization by shifting the pH to 6.6 or by addition of Mg(2+); (c) analysis of the stability of the LHC-II complex by electrophoresis in native gels demonstrated that the complex dissociates during the D transition, both at pH 7.6 and 6.6; and (d) the 77 Kelvin fluorescence maximum of LHC-II in chloroplasts was seen to shift to lower wavelengths (indicating gross denaturation of LHC-II), at the temperature of the D transition when examined at either of the above pHs. With this identification, five of the eight major endotherms of the chloroplast membrane have now been assigned.
authors: Department of Chemistry, Purdue University, West Lafayette, Indiana 47907.
authors: K A
authors: KA
authors: Smith
authors: B K
authors: BK
authors: Ardelt
authors: N P
authors: NP
authors: Huner
authors: M
authors: M
authors: Krol
authors: E
authors: E
authors: Myscich
authors: P S
authors: PS
authors: Low