The correlation between phase shifts in gradient-echo MR images and regional brain iron concentration.

The purpose of this study was to investigate the relationship between the magnetic susceptibility of brain tissue and iron concentration. Phase shifts in gradient-echo images (TE = 60 ms) were measured in 21 human subjects, (age 0.7-45 years) and compared with published values of regional brain iron concentration. Phase was correlated with brain iron concentration in putamen (R2 = 0.76), caudate (0.72), motor cortex (0.68), globus pallidus (0.59) (all p < 0.001), and frontal cortex (R2 = 0.19, p = 0.05), but not in white matter (R2 = 0.05,p = 0.34). The slope of the regression (degrees/mg iron/g tissue wet weight) varied over a narrow range from -1.2 in the globus pallidus and frontal cortex to -2.1 in the caudate. These results suggest that magnetic resonance phase reflects iron-induced differences in brain tissue susceptibility in gray matter. The lack of correlation in white matter may reflect important differences between gray and white matter in the cellular distribution and the metabolic functions of iron. Magnetic resonance phase images provide insight into the magnetic state of brain tissue and may prove to be useful in elucidating the relationship between brain iron and tissue relaxation properties.     

Improved 0/1-interchange scheduling

Consideration is given to the problem of nonpreemptively scheduling a set ofN independent tasks to a system ofM identical processors, with the objective to minimize the overall finish time. It is proved that the 0/1-INTERCHANGE scheduling heuristic can be modified, without increasing its time complexity fromO(N logM), so that its worst-case performance bound is reduced from 2 to 4/3 times optimal.     

Substrate specificity of <Emphasis Type="Italic">Streptomyces</Emphasis> transglutaminases

Transglutaminase (TGase) is a multifunctional enzyme vital for many physiologic processes, such as cell differentiation, tissue regeneration, and plant pathogenicity. The acyl transfer function of the enzyme can activate primary amines and, consequently, attach them onto a peptidyl glutamine, a reaction important for various in vivo and in vitro protein crosslinking and modification processes. To understand better the structure-function relationship of the enzyme and to develop it further as an industrial biocatalyst, we studied TGase secreted by several Streptomyces species and Phytophthora cactorum. We purified the enzyme from S. lydicus, S. platensis, S. nigrescens, S. cinnamoneus, and S. hachijoensis. The pH and temperature profiles of S. lydicus, S. platensis, and S. nigrescens TGases were determined. The specificity of S. lydicus TGase toward its acyl-accepting amine substrates was characterized. Correlation of the electronic and steric features of the substrates with their reactivity supported the mechanism previously proposed for Streptomyces mobaraensis TGase.