Plastids contain a second sec translocase system with essential functions.

Proteins that are synthesized on cytoplasmic ribosomes but function within plastids must be imported and then targeted to one of six plastid locations. Although multiple systems that target proteins to the thylakoid membranes or thylakoid lumen have been identified, a system that can direct the integration of inner envelope membrane proteins from the stroma has not been previously described. Genetics and localization studies were used to show that plastids contain two different Sec systems with distinct functions. Loss-of-function mutations in components of the previously described thylakoid-localized Sec system, designated as SCY1 (At2g18710), SECA1 (At4g01800), and SECE1 (At4g14870) in Arabidopsis (Arabidopsis thaliana), result in albino seedlings and sucrose-dependent heterotrophic growth. Loss-of-function mutations in components of the second Sec system, designated as SCY2 (At2g31530) and SECA2 (At1g21650) in Arabidopsis, result in arrest at the globular stage and embryo lethality. Promoter-swap experiments provided evidence that SCY1 and SCY2 are functionally nonredundant and perform different roles in the cell. Finally, chloroplast import and fractionation assays and immunogold localization of SCY2-green fluorescent protein fusion proteins in root tissues indicated that SCY2 is part of an envelope-localized Sec system. Our data suggest that SCY2 and SECA2 function in Sec-mediated integration and translocation processes at the inner envelope membrane.

Development and qualification of a size exclusion chromatography coupled with multiangle light scattering method for molecular weight determination of unfractionated heparin.

The molecular weight of unfractionated heparin was determined by size exclusion chromatography (SEC) coupled with multiangle light scattering (MALS) detection. The SEC/MALS method determines absolute molecular weight directly from the angular dependence of scattered light intensity as a function of concentration and does not rely on molecular weight standards for column calibration. The SEC/MALS method developed at Scientific Protein Laboratories was qualified in terms of specificity, precision, robustness, and accuracy. By eliminating the requirement of well-characterized molecular weight standards derived from heparin, the present procedure represents a clear improvement over the column calibration methods used in molecular weight determination. The SEC/MALS method is suitable for routine quality control of unfractionated heparin.

Acutrak versus Herbert screw fixation for scaphoid non-union and delayed union.

PURPOSE: To compare the treatment outcome of Acutrak versus Herbert screw fixation for scaphoid non-union and delayed union. METHODS: Records of 132 patients who underwent Herbert screw fixation (n=61) or Acutrak screw fixation (n=71) with or without bone grafting for scaphoid non-union and delayed union by a single surgeon were reviewed. The most common fracture site was the waist of the scaphoid (n=95), followed by the proximal pole (n=31) and the distal pole (n=6). Screw placement was considered accurate (n=120) when the screw was placed in the central one-third (axially) of the scaphoid; otherwise it was eccentric (n=12). Bone union was assessed radiographically and clinically. Functional outcome was assessed using the modified Mayo wrist score. RESULTS: Respectively in the Herbert and Acutrak screw groups, the mean patient ages were 25.3 and 27.3 years (p=0.28), the mean intervals between injury and screw fixation were 12.2 and 17 months (p=0.38), the mean durations to bone union were 2.1 and 1.8 months (p=0.63), and the union rates were 77% and 93% (p=0.01). The union rate was significantly higher in fractures of the waist of the scaphoid than in the proximal and distal poles (94% vs. 71% vs. 33%, p=0.001). The union rate was significantly higher when the screw was placed accurately (axially) than eccentrically (Herbert screw: 84% vs. 40%, p=0.006; Acutrak screw: 96% vs. 0%, p=0.004). 84% of the Herbert screws were placed axially, compared to 97% for the Acutrak screws. Respectively, 67% and 85% of patients had satisfactory functional outcomes (p=0.03), whereas 23% and 7% of the patients had persistent non-union (p=0.05). CONCLUSION: The Acutrak screw enabled more accurate screw placement and achieved higher union rates and modified Mayo wrist scores than the Herbert screw did.