A soluble chloroplast protein catalyzes ribulosebisphosphate carboxylase/oxygenase activation in vivo

Ribulosebisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rubisco) must be fully activated in order to catalyze the maximum rates of photosynthesis observed in plants. Activation of the isolated enzyme occurs spontaneously, but conditions required to observe full activation are inconsistent with those known to occur in illuminated chloroplasts. Genetic studies with a nutant of Arabidopsis thaliana incapable of activating rubisco linked two chloroplast polypeptides to the activation process in vivo. Using a reconstituted light activation system, it was possible to demonstrate the participation of a chloroplast protein in rubisco activation. These results indicate that a specific chloroplast enzyme, rubisco activase, catalyzes the activation of rubisco in vivo.     

RNA editing of 10 Didymium iridis mitochondrial genes and comparison with the homologous genes in Physarum polycephalum

Regions of the Didymium iridis mitochondrial genome were identified with similarity to typical mitochondrial genes; however, these regions contained numerous stop codons. We used RT-PCR and DNA sequencing to determine whether, through RNA editing, these regions were transcribed into mRNAs that could encode functional proteins. Ten putative gene regions were examined: atp1, atp6, atp8, atp9, cox1, cox2, cytb, nad4L, nad6, and nad7. The cDNA sequences of each gene could encode a functional mitochondrial protein that was highly conserved compared with homologous genes. The type of editing events and editing sequence features were very similar to those observed in the homologous genes of Physarum polycephalum, though the actual editing locations showed a variable degree of conservation. Edited sites were compared with encoded sites in D. iridis and P. polycephalum for all 10 genes. Edited sequence for a portion of the cox1 gene was available for six myxomycetes, which, when compared, showed a high degree of conservation at the protein level. Different types of editing events showed varying degrees of site conservation with C-to-U base changes being the least conserved. Several aspects of single C insertion editing events led to the preferential creation of hydrophobic amino acid codons that may help to minimize adverse effects on the resulting protein structure.     

Assessment of papain-induced lung injury in isolated lungs by measurements of aerosol deposition and mixing.

Aerosol bolus inspirations were used to assess lung injury in 15 isolated dog lungs exposed to low (0-375 units) or high doses (600-1,200 units) of papain. Effective air space size (EAD) was determined from aerosol deposition during a 5-s breath hold. Convective mixing was assessed by the spreading of the expired bolus with respect to expired volume, quantified by a coefficient of dispersion (CD) equal to the square root of the difference in the variances of the expired and inspired boluses divided by the volumetric penetration of the bolus. After exposure, CD measured with deeply penetrating boluses increased by an average of 2.5% in the low-exposure group (P greater than 0.05) and 28.0% in the high-exposure group (P less than 0.0001). CD measured with shallowly penetrating boluses decreased by 4.3% (P less than 0.0001) in the low-exposure group and increased by an average of 18.3% in the high-exposure group (P less than 0.05). Papain exposure caused EAD to increase in some lungs and decrease in others. For deep bolus penetrations, EAD changed by an average of -0.8% in the low-exposure group (P greater than 0.05) and +21.1% in the high-exposure group (P greater than 0.05). Both EAD and CD appeared to be sensitive to lung injury. However, changes in EAD were less consistent than those in CD, possibly due to changes caused by lung injury in the regional distribution of inspired aerosol.