Physical Sciences Division
Weekly Highlights for Week Ending 11/28/2001
*** Indicates item is appropriate for the HQ senior staff and may appear on the OBPR Web site: http://spaceresearch.nasa.gov
ISS FLIGHT PROGRAM
PHYSICS OF COLLOIDS IN SPACE (PCS) ON ISS: EXPPCS conducted two 48 hour runs during the past week. The first was used to study the early stage crystallization of the colloid-polymer crystal sample. The second run was used primarily to assess the current state of aging of the colloid-polymer gel sample with a 44 hour-long low angle dynamic scattering measurement. Unfortunately, because of some miscommunication of the measurement parameters between the science team and the ops team for the first 48 hour run, the run resulted in data that did not cover the proper angular scattering ranges to observe the desired behavior. Therefore, we plan to repeat this run in the near future.
MICROGRAVITY RESEARCH PROGRAM OFFICE (MRPO) PAYLOAD OPERATIONS STATUS ON THE INTERNATIONAL SPACE STATION (ISS) 7A.1 STAGE: Week 15 of Stage 7A.1 of ISS Increment 3 began with all MRPO payloads performing nominally. This will be the last week of Increment 3. Joint Operations for Increment 4 will begin with the arrival of Flight UF1 (STS-108) on 12/1/01. Crew attended operations will be significantly curtailed during the week of 11/26/01, (approximately 6 hours) due to preparations for the arrival of UF1. All necessary work for Increment 5 and 6 payloads is in full stride.
PAPER PRESENTED AT US-JAPAN CATARACT CO-OPERATIVE RESEARCH GROUP (CCRG) MEETING: Dr. Rafat Ansari (NASA GRC) presented a paper "A New Instrument for the Simultaneous Measurements of Dynamic Light Scattering and Natural Fluoresence for the Early Detection of Cataracts" at the US-Japan Cataract Co-operative Research Group (CCRG) Meeting, Hawaii, November 3-7, 2001. This paper, for the first time, presented a new instrument which combines these two powerful techniques into one single instrument for making simultaneous measurements. Preliminary data taken on human subjects was presented showing a gradual increase in the degree of natural fluorescence in the eye lens as a function of age in normal patients (20-55 years). Data was also presented on the preliminary trials of an anti-cataract agent in rats. DLS can pick up the changes one day post treatment. The conventional methods detects a mature cataract seven days post injection at which time it is impossible to intervene with a drug.
FLUID PHYSICS PI REPORTS FIRST PROTEIN CRYSTALLIZATION ON GIANT LIPID BILAYER VESCICLES: Fluid Physics Pi Prof. Alice Gast (Stanford) has successfully extended their studies of two-dimensional (2D) protein crystallization to investigate their behavior on the surfaces of giant lipid bilayer vesicles. They carried out this work in collaboration with R. Merkel and E. Sackmann at the Technical University of Munich. It is well known that some cell surfaces have densely packed organized protein coatings such as S-Layer proteins. They wished to study the influence of ordering on the surface of synthetic lipid vesicles on their mechanical properties. In particular, they have shown that streptavidin can successfully be crystallized into large domains on biotinylated vesicles. Streptavidin has previously been crystallized onto various 2D surfaces including lipid monolayers, supported lipid bilayer, lipid nanotubes, and nanometer-sized lipid vesicles. To their knowledge, this is the first report of any protein crystallization on giant lipid bilayer vesicles (typically 20-60 microns in diameter). In this study, they coated the vesicles either with pure streptavidin, or a mixture of streptavidin and the homologous non-crystallizable protein avidin. Vesicles that were coated with pure streptavidin, become covered with protein crystals. The strong interaction between the protein and the lipid membrane, in conjunction with the rigidity of 2D streptavidin crystals, distorted the vesicle shapes. The vesicles show either faceted spherical or spheroidal shapes, presumably affected by the nucleation and growth rates of individual crystallites. In either case, the vesicles exhibit viscoelastic behavior and show permanent plastic deformation when stressed beyond the yield point. The ellipsoidal vesicles show a very narrow aspect ratio (length/width) of 1.24 ± 0.11. Due to the interfering effect of gravity flattening the vesicles horizontally, the precise value of the preferred radius of curvature cannot be determined.