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Biomedical subjects

L Misra

Publications and source records attributed to L Misra.

4 recordsLinked to original sources
PubMed1984

Methodological aspects of analysing human breast cancer cell lines by NMR spectroscopy.

In an attempt to identify the factors which might affect the measurement of water proton relaxation times in cultured cells, we have begun a long-term study of two human breast cancer cell lines, MDA-MB-231 and MDA-MB-435s. We tested growth rates and cell cycle distribution as intrinsic properties of the cells as well as methodological steps which might affect the measurement of T1 and T2. A detailed examination of the growth rates of the two cell lines, easily recognized as slow (231) and fast (435s) in culture, revealed that this attribute is difficult to correlate precisely with T1s or T2s. The reason is that the relaxation times are necessarily measured at one point in time while the growth rates are a summation of ongoing processes occurring over hours. Cell cycle distribution, on the other hand, can be measured simultaneously with the relaxation times by using cells quick-frozen from the same suspension. By this method, cell cycle distribution appears to be reflected through an effect on T1s. For example, cell pellets distributed 72:15:14 in G0G1:S:G2M has longer T1s (p less than 0.01) than those distributed 43:34:23 in G0G1:S:G2M. Regarding methodological factors, trypsin appeared to lower water content and T2s in the 231 cell line. Drift in the cell cycle distribution after sample preparation did not become significant until after 2 hours in the NMR tube. It was important to standardize the force and duration of centrifugation of the cell pellets to minimize the contribution of the suspending medium without affecting cell viability. We conclude that, given careful control of methodological factors, differences in T1 may reflect metabolic differences as demonstrated by T1 differences in cell pellets showing divergent cell cycle distribution.

Breast Neoplasms↗
PubMed1981

Polymorphism of brain tubulin.

Calf brain tubulin was subjected to isoelectric focusing and tryptic peptide map analysis. Results from isoelectric focusing experiments showed a total number of 17 well-resolved protein peaks. The number of peaks and the mass distribution under each peak remained the same when the concentration of protein or ampholyte was altered. When the protein was subjected to two-dimensional isoelectric focusing, a diagonal pattern was observed, indicating that the multiple peaks observed are not a manifestation of tubulin- ampholyte interaction. Further investigation by isolating these individual subspecies and subjecting them to isoelectric focusing yielded single peaks corresponding to the original ones without generating the initial pattern of multiple peaks. Tryptic peptide maps showed that among the subspecies of the alpha subunit there are 26 spots that are common among them. There are, however, 7 +/- 1 spots that are unique in each subspecies. Similar observations were obtained for the subspecies of the beta subunit although there are only 2 +/- 1 unique spots in each subspecies. These results suggest that tubulin subunits probably consist of polypeptides with both constant and variable regions in their sequences. Identical results were obtained for canine and rabbit brain tubulin, indicating that tubulin polymorphism is common among brain tissues. Tubulin isolated by either the polymerization-depolymerization or the modified Weisenberg procedures yielded identical results. These results show that the same subspecies of tubulin are extracted by both isolation procedures.

Animals↗