A T Fojo — Page 3 | PubMed Health

PubMed1985

Amplification of DNA sequences in human multidrug-resistant KB carcinoma cells.

Four KB carcinoma cell lines selected independently for resistance to either colchicine, adriamycin, or vinblastine were studied. All cell lines showed high levels of resistance to the selecting drug and cross-resistance to the other drugs and to actinomycin D. Double-minute chromosomes could be identified on chromosomal spreads of these multidrug-resistant KB cell lines. Amplification of specific DNA sequences was demonstrated by using the technique of in-gel renaturation. All the cell lines share common amplified sequences. There are also amplified sequences that are specific for each cell line. A revertant cell line that has reacquired drug sensitivity has lost its amplified sequences. Specific probes obtained by cloning amplified sequences from the cell line selected in vinblastine recognize amplified sequences in all the resistant lines. The presence of common amplified sequences in these cell lines is strong evidence for the importance of these regions in multiple drug resistance.

Base Sequence↗

PubMed1983

Effects of acetylation and guanidination on alkaline conformations of chymotrypsin.

Guanidination leads to stabilization of several globular proteins, including bovine chymotrypsinogen, as determined by hydrogen isotope exchange (P. Cupo, W. El-Deiry, P.L. Whitney, and W.M. Awad, Jr. (1980) J. Biol. Chem. 255, 10828-10833). The present study examined the binding of proflavin to guanidinated, acetylated, and native chymotrypsins in order to compare conformational flexibilities. The order of decreasing alkaline stabilities of the catalytically active conformations of the different delta-chymotrypsin forms was guanidinated, native, and acetylated proteins; delta-chymotrypsin showed greater stability than alpha-chymotrypsin. In each case removal of calcium reduced the amount of the catalytically active conformation. The alkaline pH dependence for the decrease of the catalytically active conformation of guanidinated alpha-chymotrypsin could not be attributed to the titration of a single group, indicating that the alpha-amino group of isoleucine-16 is not the sole feature regulating the conformational transition for this derivative. At neutral pH values delta-chymotrypsin exists completely in an active conformation and the percentage of alpha-chymotrypsin in this form is only slightly lower. These differences from earlier results are possibly due to differences in buffers, calcium ion concentrations, and ionic strength. The rate of inactivation of guanidinated delta-chymotrypsin with methyl acetimidate was much lower than the corresponding rate for the native enzyme. This suggests that guanidination increases enzyme stability which in turn leads to a reduced accessibility of the alpha-amino group of isoleucine-16.

Acetylation↗