ABSTRACT
Aminotripeptidase (peptidase T) from Salmonella typhimurium and a derivative carrying a C-terminal His tag have been crystallized. In both cases, the space group was found to be C2, with a single molecule in the asymmetric unit. Crystals of the native peptidase T diffract to 2.9 A, but a selenomethionine derivative of this protein did not yield good crystals. Crystals of the His-tag peptidase T diffracted to 2.6 A, however, and could be used for the production of good-quality selenomethionine crystals. All 15 methionines, a native metal ion and two mercury reactive sites could be located and crystals suitable for MAD data collection have been produced.
Subject(s)
Aminopeptidases/chemistry , Salmonella typhimurium/enzymology , Base Sequence , Crystallization , DNA Primers , Protein ConformationABSTRACT
In order to estimate the precision and accuracy of parameters derived from segmental multiharmonic Fourier analysis of gated blood-pool images, a Monte Carlo computer noise simulation was tested on five sample regional time-activity curves. The first three Fourier harmonics were retained and the precision and accuracy of parameters of ventricular function were calculated, varying the ejection fraction, segment size, and framing rate. Precision improved with higher ejection fraction, higher counts per frame, or higher framing rate. There was no change in precision as the framing rate changed at fixed total counts. Accuracy changed little with changing framing rate. Thus, for segmental analysis there is no advantage to using a higher framing rate. Regions five or more pixels in size are recommended for reliable results. This study provides useful information for the optimization of acquisition and processing conditions for regional gated blood-pool analysis.
