The relationship between the activation state and the level of total activatable activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) was examined in tobacco protoplasts. When darkened protoplasts were illuminated, both activation and total activity increased, but at different rates; the t1,2 were 2.3 and 6.7 minutes, respectively. The light response of rubisco activation state and total activity, measured after 15 minutes of illumination, were similar but their responses to light transitions and photosynthetic inhibitors were different. When irradiance was reduced from saturating to subsaturating, deactivation of rubisco in protoplasts was immediate, whereas there was little change in total activity during the first 20 minutes following the transition. The lightinduced increases in activation state and total activity were inhibited by nigericin, but activation was more sensitive exhibiting a response similr to that of photosynthesis. Treatment of tobacco protoplasts and leaves with methyl viologen at limiting irradiance increased rubisco activation, but inhibited the light-induced increase in total activity. These results indicate that light activation of rubisco is mechanistically distinct from the light-dependent changes in total activity in tobacco, a species containing carboxyarabinitol 1-phosphate, an endogenous inhibitor of total rubisco activity.
Metabolism of 2-carboxyarabinitol l-phosphate (CA l-P), an endogenous inhibitor of ribulose. bisphosphate carboxylase/ oxygenase, occurs in the light. A soluble protein fraction which metabolized CA 1-P in the presence of NADPH was isolated from tobacco chloroplasts. A similar fraction from spinach exhibited much lower activity. The activity in tobacco extracts was stable overnight at 4°C but its maintenance during storage required dithiothreitol. The tobacco protein responsible for CA 1-P metabolism was partially purified by ion-exchange FPLC of stromal extracts. The requirements for NADPH and dithiothreitol for activity of this protein suggest a mechanism for the light-dependent control of CA 1-P levels in plants.
This study was performed to evaluate the importance of the duration of balloon inflation during PTCA, by comparing two common inflation durations. Patients were randomized to a 30-second inflation protocol (group I, 83 procedures, 109 lesions), or a 60-second protocol (group II, 83 procedures, 115 lesions). There were no differences in baseline characteristics between the two groups, and no subsequent differences in mean inflation number (3.4 +/- 1.6 vs 3.1 +/- 1.6), residual stenosis (34% +/- 17% vs 33% +/- 16%), presence of dissection (29% vs 34%), or clinical success (89% vs 84%), group I versus group II, respectively. The 30-second inflations caused significantly less chest pain score (147 +/- 239 vs 399 +/- 516, P less than 0.001), and ST segment alteration (75 +/- 94 seconds vs 136 +/- 163, P less than 0.05). These results indicate that 60-second inflations do not produce a superior result to 30-second inflations. Furthermore, shorter inflations are much better tolerated.
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