The lack of correlation between the degree of sprouting and the a-amylase activity in wheat and rye, as well as the apparent variation in the falling number during ripening, can be explained as the result of two amylase systems acting during different stages of the development of the grain. During the early stages of the development of the grain, a-amylase is continuously inactivated. This process is reversible, however, and when the evaporation of moisture is retarded the a-amylase activity increases as a consequence of the higher amount of dissolved enzyme. This results in an occasional decrease in the falling number, which might amount to more than 50 sec. During germination, a new kind of a-amylase develops. The synthesis of the new form of a-amylase is irreversible and causes a much greater and permanent reduction in the falling number. During the initial stages of germination, the amylase activity thus increases owing to the combined action of both the original amylase and the new form. The two kinds of amylases show different electrophoretic patterns. Drying the grain after harvesting reduces the activity of 'green' amylase (amylase in unripened grain), which might explain the frequent observations of increasing falling number during storage.
By introducing an Einzel lens in the field-free region of a straight time-of-flight mass spectrometer, secondary ions of large mass can be detected more efficiently in plasma-desorption mass spectrometry. This procedure compensates for the large radial velocities of large molecular ions recently observed experimentally. It is shown that large molecular ions like those of lysozyme can now be detected more efficiently, and larger molecular ions than observed before in plasma-desorption mass spectrometry (like those of bovine ovalbumin, mol. wt 45 000) can now be studied.The mechanism for ejection of intact, organic, molecular ions by particle impact has attracted a lot of interest in recent years. In particular, the understanding of the ejection process in electronic sputtering of organic molecules has improved considerably. Electronic sputtering is the process whereby a fast, heavy ion, such as a fission fragment, causes ejection from a surface. This is the ejection process operative in plasma-desorption mass spectrometry (PDMS). ' The total erosion yield of intact, neutral molecules when a fission fragment hits a sample of amino acids is of the order of one thousand.' When the fast ion hits the organic surface a crater is f~r m e d .~The yield of intact molecules scales as the third power of the energy deposited in the sample ~u r f a c e .~ Furthermore, it has been shown that large molecular ions leave the surface in the ejection process with an angle related to the direction of the incident fast ion.' This can be interpreted as the molecule being pushed out by a cylindrical expanding ion track caused by the fast ion. The detailed mechanism for this expansion is debated but low-energy electrons exciting low-lying vibrational levels in the large organic molecule is a "soft" way of achieving this expansion.6 The scaling of the yields of neutral species and the non-normal ejection of large molecules have been reproduced in a molecular dynamics simulation by Fenyo et ~1 .~ Recently, Johnson et u L .~ have also formulated an analytical model for socalled pressure-pulse sputtering which gives a rationale for the ejection of intact large organic molecules by sputtering with a particle creating a high energy density track, such as a fission fragment. The non-normal ejection found by Ens et u Z .~ has consequences for the construction of a spectrometer to observe large molecular ions in PDMS. If, for example, the fission fragments 'Author to whom correspondence should be addressed.enter the sample foil from behind, as in most plasmadesorption mass spectrometers, the large molecular ion will "avoid" the normal direction. If the flight tube is long this will have the effect that most molecular ions miss the stop detector. There are two obvious ways to compensate for this effect: one is to use an electrostatic guide wire as used by Chait et ~1 .~The original intention with this first solution was to suppress neutral species by using a long flight-tube. The obvious alternative is to use an Einzel lens; this alternative has...
Samples for plasma desorption mass spectrometry (PDMS)' were originally prepared by simply depositing a droplet of the substance to be examined dissolved in a solvent onto an aluminium foil, but the electrospray method2 quickly succeeded the droplet technique.A few years ago, adsorption to polymer backings was introduced as a sample preparation method by Jordon et al. 334 In 1985, a new and promising substrate material was discovered by Jonsson et ul. ,' namely nitrocellulose. It is now widely used by many groups. Even though nitrocellulose has been used by biochemists for years, the binding mechanisms of proteins to it are poorly understood. The present experiment demonstrates a method of studying this interaction by examining how the yield (number of detected secondary ions per incoming primary ion) varies with the amount of biomolecular sample deposited on the nitrocellulose backing. EXPERIMENTAL Sample preparationThree small proteins, bovine insulin (mol.wt 5733), pancreatic spasholytic peptide (PSP, mol.wt 11711) and porcine trypsin (mol.wt 23463), were used in the experiment. The sample material was dissolved in a mixture of 50% of 0.1% trifluoroacetic acid (TFA) solution (1 LTFA-solution is 1 mL trifluoroacetic acid 999mLH20) and 50% of 95% ethanol (i:l, vh). A series of dilutions was made for each type of molecule. A known amount of sample, in a droplet of 3 p L (Fig. 1), was placed on a small circular area ( d i a m e t e r 4 mm) of nitrocellulose electrosprayed onto silicon.' One minute after deposition of a droplet the nitrocellulose samples were washed 5 times with a jet of 0.1% TFA solution using a Pasteur pipette. The samples were dried with clean air and loaded into the experimental chamber of the spectrometer.A test of how long it takes for the molecules to bind to the nitrocellulose backing was also made in order to find the best conditions for the experiment. For this purpose insulin was used and the time between deposition of sample solution and washing was varied over a time range of 0-7min (at this time the solution was dried in to the sample). From this test a rest time of 1 min was chosen between deposition and washing.' Author to whom corrcspondencc should hc adctrcsscd. Positive ion PDMS-spectra of bovine insulin (mol.wt 5733). The upper spectrum was run for 1 h (1.4x I0"start pulses), the other spectra werc run for 10 min (2.4~10" start pulses). In all spectra, except the upper one, the amount of sample deposited onto the nitrocellulose surface before washing is indicated. The spectrometerIn the time-of-flight spectrometer used in this experiment (Fig. 2), the samples are bombarded from the front with fission fragments from a zs2Cf source. The source is placed hetween the sample and the start detector near to the sample at an angle of 45". One fission fragment hits the sample and the other is used to create a start signal in the start detector. The desorbed secondary ions are accelerated in a gap of approximately S mm and the field-free region is approximately 15 cm long. The stop detec...
Secondary ions from solid samples of bovine insulin (5733 u) have been produced by bombardment with particles in the high energy (∼MeV/u) and low energy (∼keV/u) regime. Radial velocity distributions were measured in time-of-flight mass spectrometers with deflection plates in the field-free flight tube. For high energy bombardment the average angle of ejection for molecular ions was found to be correlated to the incident ion direction. The results suggest that there is an outward momentum transfer, like a mechanical pressure wave, from the expanding fast ion track to large molecular ions. In contrast, the angular distribution of molecular ions ejected by low energy bombardment seems to be independent of the primary ion direction
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