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Ira D. Bhattacharya M. F. Picciano John A. Milner 《Biological trace element research》1988,18(1):59-70
Human milk glutathione peroxidase (GPx) was purified 4500-fold using acetone precipitation and purification by repetitive
ion-exchange and gel filtration chromatography with an overall yield of 34%. Homogeneity was established by gel electrophoresis.
Using gel filtration, the molecular weight (mol wt) of the enzyme was estimated to be 92 kdalton (kD). The monomeric molecular
weight was estimated to b 23 kD from polyacrylamide gel electrophoresis, indicating that the native enzyme consists of four
identical subunits. The molecular weight of each subunit was supported by amino acid analysis. Selenium (Se) content of the
purified enzyme was 0.31%, in a stoichiometry of 3.7 g-atoms/mol. Data from these studies reveal that GPx provided approximately
22% of total milk Se, but only 0.025% of the total protein. 相似文献
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Summary Different staining procedures, various digestion methods and autoradiographic techniques were employed to study the structure and composition of the nucleolus and of the nucleolonema, after unmasking the latter by adenosine treatment. The presence of DNA, RNA, protein and lipid in these structures has been shown. It has been demonstrated that the filamentous structure within the nucleolus — the nucleolonema— has a core of DNA, around which RNA and protein have accumulated. The structure of the nucleolonema suggests that it is in a highly active state, in synthesizing ribosomal RNA and protein.We take the opportunity to express our gratefulness to the Director, Prof. Dr. Hans Lettré, for providing facilities to work in this Institute. We like to thank our other colleagues, particularly Dr. N. Paweletz, for their valuable help during the course of the investigations. 相似文献
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Adrie Ykema Elizabeth C. Verbree Ira I. G. S. Verwoert Karin H. van der Linden H. John J. Nijkamp Henk Smit 《Applied microbiology and biotechnology》1990,33(2):176-182
Summary From six unsaturated fatty acid auxotrophs (Ufa mutants) of the oleaginous yeast Apiotrichum curvatum blocked in the conversion of stearic to oleic acid, were isolated revertants able to grow in the absence of unsaturated fatty acids, in a search for strains that can produce cocoa butter equivalents. A broad range in the percentage of saturated fatty acids (%SFA) was observed in the lipids of individual revertants (varying from 27%–86% SFA), compared with the wild-type (44% SFA). Further analysis of fatty acid composition indicated that: (i) not all six Ufa mutants had the same genetic background and (ii) one specific Ufa mutation could be reverted in more than one way. Revertants that produced lipids with a %SFA>56%, were examined further. These strains were cultivated for 50 generations and half of them produced lipids with high %SFA after that time and were defined as stable. The viability of revertant strains with extremely high %SFA (>80%) may be explained by our finding that polar lipids, which are part of yeast membranes, contained much more polyunsaturated fatty acids and a significantly lower %SFA than neutral (storage) lipids. One revertant (R25.75) was selected that was able to produce lipids in whey permeate at a rate comparable with wild-type A. curvatum and with a fatty acid composition and congelation curve comparable with cocoa butter.
Offprint requests to: A. Ykema 相似文献
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Gregory M. L. Patterson Kathleen K. Baker Cynthia L. Baldwin Christine M. Bolis Faith R. Caplan Linda K. Larsen Ira A. Levine Richard E. Moore E. Moore Carrie S. Nelson Kathryn D. Tschappat Grace D. Tuang Michael R. Boyd John H. Cardellina Ralph P. Collins Kirk R. Gustafson Kenneth M. Snader Owen S. Weislow Ralph A. Lewin 《Journal of phycology》1993,29(1):125-130
Lipophilic and hydrophilic extracts from approximately 600 strains of cultured cyanophytes, representing some 300 species, were examined for antiviral activity against three pathogenic viruses. Approximately 10% of the cultures produced substances that caused significant reduction in cytopathic effect normally associated with viral infection. The screening program identified the order Chroococcales as commonly producing antiviral agents. 相似文献
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Molecular cloning and sequencing of infC, the gene encoding translation initiation factor IF3, from four enterobacterial species 总被引:3,自引:0,他引:3
Dionysios Liveris John J. Schwartz Robert Geertman Ira Schwartz 《FEMS microbiology letters》1993,112(2):211-216
Abstract Translation initiation factor IF3 plays a crucial role in initiation of protein synthesis in bacteria. In order to elucidate the IF3 structural elements required for these functions, the evolutionary conservation of IF3 and its gene, infC , was investigated. Homologous infC sequences from Salmonella typhimurium, Klebsiella pneumoniae, Serratia marcescens and Proteus vulgaris were amplified by the polymerase chain reaction and sequenced. Analysis of these sequences, as well as that from Bacillus stearothermophilus , revealed several regions (e.g. residues 62–73 and 173–177) of absolute sequence conservation, suggesting an important role for these regions in IF3 function. 相似文献
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Ursula A. Germann Timothy C. Chambers Suresh V. Ambudkar Ira Pastan Michael M. Gottesman 《Journal of bioenergetics and biomembranes》1995,27(1):53-61
Cells expressing elevated levels of the membrane phosphoprotein P-glycoprotein exhibit a multidrug resistance phenotype. Studies involving protein kinase activators and inhibitors have implied that covalent modification of P-glycoprotein by phosphorylation may modulate its biological activity as a multidrug transporter. Most of these reagents, however, have additional mechanisms of action and may alter drug accumulation within multidrug resistant cells independent of, or in addition to their effects on the state of phosphorylation of P-glycoprotein. The protein kinase(s) responsible for P-glycoprotein phosphorylation has(ve) not been unambiguously identified, although several possible candidates have been suggested. Recent biochemical analyses demonstrate that the major sites of phosphorylation are clustered within the linker region that connects the two homologous halves of P-glycoprotein. Mutational analyses have been initiated to confirm this finding. Preliminary data obtained from phosphorylation- and dephosphorylation-defective mutants suggest that phosphorylation of P-glycoprotein is not essential to confer multidrug resistance. 相似文献
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The distribution of aphidicolin-induced chromosomal lesions was analyzed to determine the relative breakage susceptibility of euchromatin and heterochromatin in the cactus mouse, Peromyscus eremicus. The observed breakage was tested against expected distributions corresponding to the karyotypic proportions of autosomal euchromatin, autosomal heterochromatin, X-chromosomal euchromatin, and X-chromosomal heterochromatin. The distribution of induced breakage was independent of sex but dependent on the individual. In all individuals, there was a highly significant (P0.0001) deficiency in the number of breaks observed as compared to expected in autosomal heterochromatin. Sparse observations in the X chromosome and the absence of breaks in the Y chromosome precluded valid statistical tests of the sex-chromosomal distribution of induced breakage. These data indicate that the autosomal heterochromatin of Peromyscus is resistant to aphidicolin-induced chromosomal breakage and argue against a simple relationship between late replication and a general mechanism for chromosomal fragility. 相似文献