Biomedical subjects

M I Lerman

Publications and source records attributed to M I Lerman.

At least 181 records · Page 10Linked to original sources

PubMed1976

Loosening and unfolding of E. coli 50 S ribosomal subunits: dependence on magnesium content and temperature.

Reversible change of 50 S ribosomal subunits to 40 S particles takes place in cold buffered 0.5 M NH4Cl solutions either containing Mg++ (up to 0.1 M), or free from Mg++ and even supplemented with EDTA (1 mM). The 40 S particles were stable only within a definite temperature range. Heating of the samples caused completely irreversible unfolding of the 40 S particles. This "melting" appeared to be co-operative and took place within a very narrow range of temperature, which for samples containing Mg++ was a linear function of the log of Mg++ concentration. The results suggest that two types of bonds maintained the compact structure of the ribosomal subunits: ionic bonds involving Mg++ and heat-labile weak interactions between ribosomal components.

Chemical Phenomena↗

PubMed1976

[In vitro incorporation of labelled amino acids into heart muscle ribosomes at early and late stages of compensatory heart hyperfunction].

The activity of a protein-synthesizing cell-free system from heart muscle was studied at early and late stages of compensatory heart hyperfunction. It was found that the incorporation of amino acids into heart ribosomes during 48 hours after the hyperfunction had been produced, increased by 30% as compared to the control. The incorporation of amino acids into heart ribosomes at the late stage of hyperfunction (after 6 months) was decreased by 46% as compared to the early stages. The addition of homologous tRNA to the cell-free system of protein synthesis under prolonged heart hyperfunction stimulated the incorporation of amino acids into the ribosomes by 40--50%.

Amino Acids↗

PubMed1976

The limiting effect of transfer RNA's on the rate of protein synthesis in cell extracts of rapidly growing tumors.

Using crude cell extracts from rapidly growing animal and human tumors, we found that (a) the addition of homologous transfer RNA (tRNA) to these extracts stimulated polypeptide synthesis two-to threefold, while addition of heterologous tRNA did not have a similar effect; (b) addition of homologous as well as heterologous ribosomal RNA was also stimulatory; and (c) both stimulatory effects were additive. The possibility that the effect of homologous tRNA could be mediated by contaminating material (such as the "translational control" RNA) seems to be rulted out by experiments with highly purified tRNA preparations, which did not contain even traces of 18 S, 7 S, 5 S, and smaller than 4S RNA's. Control experiments showed that no loss of tRNA occurred either during preparation of the cell extracts or under the conditions of in vitro protein synthesis. The results obtained suggest possible occurrence of a deficiency in specific isoaccepting tRNA's in rapidly growing solid tumors.

Animals↗

PubMed1976

[Analysis of macromolecule alkylation in tissues of intact and tumor carrying mice].

Alkylation DNA reparation kinetics and the disintegration of alkylated RNA, proteins and lipids in liver, spleen and brain of intact and 22A hepatomic mice after a injection of 1-14C-nitrosomethylurea at a therapeutic dose are studied. The tissue studied are different in their macromolecules and lipids alkylation, in DNA reparation and RNA, protein and lipid degradation rates. Possible correlation between the time of the occurrence of DNA damages and the frequency of tumour emergence in different tissues is discussed. It is found that normal cells eliminate more rapidly degraded RNA, protein and lipid molecules and more rapidly repair DNA damages as compared with 22A hepatoma cells. It is suggested to be due to more rapid macromolecule metabolism in normal cells which specifies a selective sensitivity of tumour cells to alkylating agents and nitrosoalkylureas. The time of the occurrence of damages induced with alkylating agents and nitrosomethylureas is supposed to be a critical parameter in processes resulting in the selective sensitivity of normal and tumour cells.

Alkylation↗

PubMed1975

Three mRNA populations differing in turnover and processing in mouse liver.

Using kinetics of approach to steady state labeling, we have found that liver poly(A)+ mRNAs fall into three populations, differing in stability and probably in processing, as reflected in their dissimilar delays in reaching polyribosomes and turnover times. There are mRNA-1 (delay 10 min, half-life 1 hr); mRNA-2(delay 3 hr, half-life 2 hr); and mRNA-3 (delay 40 min, half-life 2.6 hr). The first two species function on free polyribosomes while the third one is operating on bound polyribosomes. The populations listed contribute 10,20 and 70%, respectively, to the total steady state labeled poly (A)+ mRNAs.

Animals↗

PubMed1975