Absorptive Mode Research Articles

Amylase as an extracellular enzyme from plasmodia of myxomycetes

In the course of our studies on the nature of the relationship between plasmodia of myxomycetes and their bacterial associates, we found that the plasmodia of Physarum flavicomum and Stemonitis herbatica were able to degrade starch in starch agar plates, whereas their bacterial associates Flavobacterium breve and Paracoccus denitrificans in pure culture could not do so, suggesting a dependence of bacterial associate on the plasmodium for utilization of a complex substrate. Further, a wide zone of starch clearance around the plasmodium in P. flavicomum indicated that the enzyme was extracellular. The significance of this finding is that the production of extracellular amylase by myxomycetes is being reported for the first time, and it suggests that the myxomycetes may have an absorptive mode of nutrition besides the ingestive or holozoic mode generally ascribed to them.

Phase-sensitive heteronuclear multiple-bond correlation in the presence of modest homonuclear coupling. Application to distamycin A

Long-range correlation of proton and heteronuclear chemical shifts, in particular carbon, has proven invaluable in the investigation of mo lecular structure ( I7). The advent of indirect detection of heteronuclei via protons has made long-range correlation routine even on low concentration samples. The most useful indirect technique for long-range correlation proposed thus far is the heteronuclear mu ltiple-bond correlation (HMBC) experiment ( 7). We have used this technique with excellent results despite the fact that we use the proton-decoupl ing coil of our standard Varian 5 m m broadband switchable probe for observation. Typically, we achieve a nominal fivefold increase in signal-to-noise ratio (S/N) per unit measur ing time compared to the 13C detected experiment. We have recently encountered difficult assignment problems via work with analogs of the DNA-binding drug distamycin A (8-l 1) . These problems are due to low sensitivity and poor proton resolution. Distamycin A, for instance, shows a significant degree of aromatic proton overlap in its ‘H spectrum (Table 1) . Also, complete assignment of the 13C and ‘H spectra requires correlation of carbonyl resonances with aromatic ring protons via 4 JCH which is quite small, requiring the highest sensitivity possible. The sensitivity of HMBC has been addressed by Bax and Marion ( 12). They proposed a m ixed mode data-processing procedure for the HMBC experiment, which utilizes a hypercomplex Fourier transform (13) of the data, resulting in absorptive mode in F, followed by a magn itude calculation in F2. This technique results in a \Iz increase in S/N. The reason for applying a F2 magn itude calculation to the HMBC data in both the conventional method and Bax and Marion’s experiment is the presence of phase modu lation of the F2 data by proton chemical shift and homonuclear coupling during the delay, 7, in F ig. la. Since distamycin A and its congeners show only modest (e.g., 2 Hz) scalar coupling in the over lapped aromatic ‘H region, it seemed that the m inimal amount of phase modu lation due to these couplings m ight

How modern systematics relates to the rumen fungi

The zoosporic fungi comprise a polyphyletic grouping of four classes, the Plasmodiophoromycetes, Oomycetes, Hyphochytriomycetes and Chytridiomycetes. Apart from their absorptive mode of nutrition and the presence of zoospores in some stage of their life cycle, there is little these classes have in common. The zoosporic species of rumen fungi are classified in the Class Chytridlamycetes which is a monophyletic group with extreme diversity in thallus morphology, reproduction and zoospore cytology. The rumen fungi have many characteristics in common with the Spizellomycetaceae but have been given their own family, the Neocallimasticaceae. There are arguments for reducing this family to synonymy with the Spizellomycetaceae, or elevating it to a new order, but before a rational decision can be made, more rumen fungi require detailed examination, especially their zoospore ultrastructure.

The Dual Absorptive Mode and πp Elastic Scattering Revisited

Using the Regge pole phase rule for contributions to both amplitudes the DAM is applied to πp elastic scattering in the plab≥10 GeV/c and |t|≤0.8(GeV/c)2 region. It is found that the DAM has a mixed success in describing πp scattering. The ρ contribution to both amplitudes is in accord with the DAM while the f- non-flip contribution does not have a peripheral zero. The Pomeron imaginary part is in accord with the DAM with a non-negligible Pomeron phase so that the DAM approximation Rep=0 is unsatisfactory. There is also a Pomeron-flip contribution contrary to the expectation of the model. The σ-flip contribution is taken into account and a small f-flip contribution i s also required.

A new H10-to-H20 mode transducer

Using a general method of mode-transducer design previously described, a simple H10-to-H20 mode transducer was constructed. The reflection coefficient is calculated, and it is shown that for a transducer a few wavelengths in length the reflections are insignificant. The power transferred to the spurious modes was measured by the resonance method on two experimental models, 2 and 8 guide-wavelengths long. The longer transducer transforms 92% of the power into the required mode. The power in unwanted modes can be greatly reduced by the use of a simple absorptive mode filter.