The kinetics of the isoprene-OH/OD reaction in the presence of O 2 and NO have been studied using laser photolysis/laser-induced fluorescence. We report pressure and temperature-dependent rate constants for the addition of OH/OD to isoprene are in good agreement with previous studies. On the basis of simulations to OH cycling curves, we find a value of (9.0 ( 3.0) × 10 -12 molecule -1 cm 3 s -1 for the overall reaction rate constant of hydroxy peroxy radical with NO at 298 K. We report a rate constant for O 2 addition to the hydroxy alkyl radical of (2.3 ( 2.0) × 10 -12 molecule -1 cm 3 s -1 at 298 K. We find little generation of OH from the OD initiated oxidation of isoprene, and no significant differences in OH and OD cycling, suggesting that H-shift isomerization is the major pathway for δ-hydroxy alkoxy radicals, in agreement with theoretical predictions.

Vastly different folded transmembrane segments of nascent multispanning membrane proteins each induce structural changes in the ribosome tunnel and translocon that target the loops of the growing polypeptide alternately into the cytosol or ER lumen.

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