binding of either tyrosine or 6MPH4 alone does not change the coordination. However,
when both tyrosine and 6MPH4 are bound, the active site becomes 5-coordinate, creating
an open site for reaction with O2. Investigation of the kinetics of oxygen reactivity of
TyrH complexes in the absence and presence of tyrosine and/or 6MPH4 indicated that
there is a significant enhancement in reactivity in the 5-coordinate complex in
comparison to the 6-coordinate form. Similar investigations with E332A TyrH showed
that Glu332 residue plays a role in directing the protonation of the bridged complex that
forms prior to the formation of Fe(IV)O.
Rapid chemical quench analyses of DOPA formation showed a burst of product
formation, suggesting a slow product release step. Steady-state viscosity experiments
established a diffusional step as being significantly rate-limiting. Further studies with
stopped-flow spectroscopy indicated that the rate of TyrH reaction is determined by a
combination of a number of physical and chemical steps.
Investigation of the NO complexes of TyrH by means of optical absorption,
electron paramagnetic resonance (EPR) and electron spin echo envelope modulation
(ESEEM) techniques revealed the relative positions of the substrate and cofactor with
respect to NO, an O2 mimic, and provided further insight into how the active site is
tuned for catalytic reactivity upon substrate and cofactor binding.
The second theory is that a decreased vertical temperature lapse rate, dT/dp, would slow cloud growth, creating a mode of cloud-top heights at the stable layer as clouds lose buoyancy. The signal for lapse rate changes in the AIRS data, however, is not as strong as the signal for RH differences. Near 600-400 hPa, roughly the region where congestus cloud-top heights are located, no significant difference in lapse rates is noted between congestus and deep clouds; in fact, the mean values suggest that congestus clouds appear in more unstable atmospheres than deep clouds. Only slight differences in temperature and lapse rate are noted in ERA data as well. These results suggest that drier air may play a greater role in limiting congestus cloud-top heights than increased atmospheric stability.
Five years of relative humidity (RH) observations from the Atmospheric Infrared Sounder (AIRS) instrument aboard the Aqua satellite are then analyzed to identify areas of anomalously dry air between 600 and 400 hPa over deep convective regions of the tropical oceans. Back trajectories are then calculated for each observed parcel.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-12-7396 |
| Date | 2009 December 1900 |
| Creators | Casey, Sean P. |
| Contributors | Dessler, Andrew E. |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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