Improved analysis of ultra-high molecular mass polystyrenes in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using DCTB matrix and caesium salts.

RATIONALE: The ionization of polystyrenes in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is typically achieved by the use of silver salts. Since silver salts can cause severe problems, such as cluster formation, fragmentation of polymer chains and end group cleavage, their substitution by alkali salts is highly desirable. METHODS: The influence of various cations (Ag(+), Cs(+) and Rb(+)) on the MALDI process of polystyrene (PS) mixtures and high mass polystyrenes was examined. The sample preparation was kept as straightforward as possible. Consequently, no recrystallization or other cleaning procedures were applied. RESULTS: The investigation of a polystyrene mixture showed that higher molecular polystyrenes could be more easily ionized using caesium, rather than rubidium or silver salts. In combination with the use of DCTB as matrix a high-mass polymer analysis could be achieved, which was demonstrated by the detection of a 1.1 MDa PS. CONCLUSIONS: A fast, simple and robust MALDI sample preparation method for the analysis of ultra-high molecular weight polystyrenes based on the use of DCTB and caesium salts has been presented. The suitability of the presented method has been validated by using different mass spectrometers and detectors.

Blood clotting factor IX. Loss of activity after cleavage of sialic acid residues.

Enzymatic cleavage of sialic acid from human blood clotting factor IX results in a loss of factor IX clotting activity. The loss of clotting activity and the rate of release of sialic acid follow the same time courses. Control experiments have ruled out several explanations for the loss of factor IX activity: proteolytic degradation, inhibitory effects of free sialic acid, and non-specific inhibition of the clotting assays. Furthermore, no inhibition was seen when similar enzymatic cleavage was carried out on factor X and factor VIII. Therefore, we suggest that the loss of factor IX activity is the direct result of cleavage of sialic acid from the protein. Most of the inhibition appeared to be an effect on the activity of factor IXa itself, and thus far, little or no effect has been shown on the activation of factor IX to IXa. The structural basis for this unusual effect of sialic acid on protein function currently is being investigated.