BchI, belonging to the AAA+ -protein family, forms the enzyme magnesium chelatase together with BchD and BchH. This enzyme catalyses the insertion of Mg2+ into protoporphyrin IX upon ATP hydrolysis. Previous studies have indicated that BchI forms ATP-dependent complexes and it is a member of the AAA+ -protein family (ATPases associated with various cellular activities) and it was suggested based on structural homology that the BchI formed hexameric complexes. AAA+ -proteins are Mg2+ -dependent ATPases that normally form oligomeric ring complexes in the presence of ATP. Single particle analysis of fully formed ring complexes of BchI observed by negative staining EM indicate that the BchI has strong 6- and 2-fold rotational symmetries and a weaker 4-fold rotational symmetry which are reminiscent of DNA helicase. A 2D average of the fully formed BchI-ATP ring complex is presented here from images of the complex obtained from negative staining EM. Other complexes are also observed in the EM micrographs and the class averages of these are indicative of the fragility and dynamic nature of the BchI complex which has been reported and they are suggestive of partially circular complexes with six or less protomers per particle. The resolution of the average circular complex is estimated at approximately 30A and it is similar in shape and size to an atomic resolution hexameric model of BchI rendered at 30A.

Adenosine Triphosphatases↗

PubMedDate not supplied

Operant acuity of toddlers and developmentally delayed children with low vision.

The present report describes an operant procedure for the assessment of grating acuity in young and/or developmentally delayed children. Prior to testing, the child was trained to point to a grating presented on one of two equally bright screens. A reward was given to the child for each correct response. During the test, the gratings became progressively finer until the child no longer made consistently correct choices. Normative data from 90 children show improvement in grating acuity during years one to five (from 20/50 to 20/17). Results were also obtained from 100 consecutive pediatric patients who were thought to be visually unresponsive or visually impaired by the referring ophthalmologist. Overall, 12% of these children tested within the normal range, 53% had grating acuities better than 20/200 but below normal, 27% had acuities below 20/200, and 8% were not measurable. These results suggest that a wide range of visual potential exists in this population and that some of these children may benefit from visual aids and training.

Adolescent↗

PubMedDate not supplied

Breast-feeding and optimal visual development.

The goal of the present study was to determine whether dietary supply of omega-3 essential fatty acid (EFA) influences visual development in healthy pre-term and full-term infants. Visual status was examined in human milk-fed infants (ample dietary omega-3 EFA supply) and corn oil-based formula-fed infants (no dietary omega-3 EFA; standard formula prior to 1987). At 57 weeks postconception (4 months adjusted age), both pre-term and full-term human milk-fed infants had significantly better visual evoked potential (VEP) and forced-choice preferential-looking (FPL) acuity than formula-fed infants. Acuity was correlated with a dietary omega-3 sufficiency index from red blood cell membranes obtained at 57 weeks postconception. At 36 months, full-term human milk-fed children had significantly better random dot stereo acuity and letter matching ability than formula-fed children. Stereo acuity and performance on the letter matching test were correlated with a dietary omega-3 sufficiency index from red blood cell membranes obtained at 4 months. These results suggest that dietary omega-3 fatty acids play an important role in visual development.

Breast Feeding↗