EN
The effect of dehydration on the lamellar spacing
of photosystem II (PS II) membrane fragments from
spinach has been investigated using neutron membrane
diffraction at room temperature. The diffraction data reveal
a major peak at a scattering vector Q of 0.049 Å−1
at a relative humidity (r.h.) of 90% corresponding to a
repeat distance D of about 129 Å. Upon dehydration to
44% r.h., this peak shifts to about 0.060 Å−1 corresponding
to a distance of 104.7±2.5 Å. Within experimental error,
the latter repeat distance remains almost the same
at hydration levels below 44% r.h. indicating that most
of the hydration water is removed. This result is consistent
with the earlier finding that hydration-induced conformational
protein motions in PS II membrane fragments
are observed above 44% r.h. and correlated with the onset
electron transfer in PS II (Pieper et al. 2008, Eur. Biophys.
J. 37: 657–663).