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K B Freeman

Publications and source records attributed to K B Freeman.

81 records · Page 5Linked to original sources
PubMed1969

Importance of the osmolarity of the incubation medium on amino acid incorporation into protein by isolated rat liver mitochondria.

1. Incorporation of [(14)C]leucine into protein by isolated rat liver mitochondria was examined by using incubation media similar to those used by Sandell, Löw & Decken (1967) (medium A) and Roodyn, Reis & Work (1961) (medium B). The incorporation process was found to be almost completely inhibited in medium A. 2. By decreasing the amount of sucrose and omitting tris-hydrochloric acid from medium A, incorporation proceeded at a rate higher than that found in medium B. It was found that the inhibitory action of medium A was due to its high osmolarity. 3. Oxidative phosphorylation and RNA synthesis by the isolated mitochondria proceeded at the same rate in media essentially the same as media A and B. 4. There was a partial inhibitory action of medium A on leucine uptake by the mitochondria and also on the formation of leucyl-transfer-RNA. The major block of inhibition by the hyperosmolarity of medium A seemed to be located at a later step of protein synthesis involving mitochondrial ribosomes. 5. Protein synthesis by Escherichia coli B was only slightly inhibited, if at all, in hyperosmotic media in which protein synthesis by isolated mitochondria was completely stopped.

Animals↗
PubMed1967

The site of synthesis of mitochondrial proteins in Krebs II ascites-tumour cells.

At 22 degrees in Earle's medium, Krebs cells synthesize proteins. After a brief ;pulse' with [(14)C]valine followed by a ;chase' of [(12)C]valine the radioactivity appears first in microsomes and is transferred after ;chase' to the cell sap. Kinetics of labelling of the mitochondrial protein are different from that of either microsomal or cell-sap protein. When Krebs cells in buffer are mixed with ribonuclease in water the nuclease penetrates the cell membrane. The ribonuclease-treated cells are still viable but have lost most of their cytoplasmic ribosomes (electron micrograph). Such cells still synthesize mitochondrial protein at near normal rate but synthesis of microsomal protein is severely inhibited. The results indicate that some mitochondrial proteins are synthesized independently of the microsome-cell-sap system.

Journal Article↗
PubMed1967

The morphological site of synthesis of cytochrome c in mammalian cells (Krebs cells).

In Krebs ascites-tumour cells, cytochrome c is segregated in the mitochondria and the level in microsomes could not be measured. At 22 degrees in glucose-buffer Krebs cells synthesized a spectrum of proteins including cytochrome c. Mild osmotic shock in the presence of ribonuclease had little effect on incorporation of [(14)C]-leucine or [(14)C]valine into mixed mitochondrial protein but strongly inhibited synthesis of non-mitochondrial cytoplasmic proteins. Under these conditions, labelling of cytochrome c was also strongly inhibited. After pulse labelling of Krebs cells at 22 degrees for 10min. the cytcchrome radioactivity found in mitochondria was higher than in microsomes. After addition of unlabelled amino acid as ;chase' there was 137% increase in radioactivity of cytochrome c but only a 3% increase in radioactivity of whole-cell protein. It is concluded that the peptide chain of cytochome c is synthesized on cytoplasmic ribosomes. Mitochondria therefore do not have the character of self-replicating entities, but are formed by the cooperative function of messenger RNA of cytoplasmic ribosomes and, possibly, of intramitochondrial messenger derived from the mitochondrial DNA.

Journal Article↗
PubMedDate not supplied

Effects of exposure temperature on brown adipose tissue uncoupling protein mRNA levels.

The effect of temperature on the amount of uncoupling protein mRNA in rat brown adipose tissue was examined after 1 and 14 days of exposure to cold. The relative amounts after 1 day, compared with rats kept at a thermoneutral temperature of 28 degrees C, were 3.2 at 19 degrees C, 3.3 at 11 degrees C, and 2.1 at 3 degrees C. This suggests that in warm-acclimated rats, a maximal response to a cold stimulus in brown adipose tissue is reached by 19 degrees C. In contrast to these results, the relative amounts of uncoupling protein mRNA after 14 days of cold exposure, compared with rats left at 28 degrees C, were 1.2 at 19 degrees C, 1.9 at 11 degrees C, and 2.1 at 3 degrees C. Since it is known that the amount of uncoupling protein in cold-acclimated rats increases continuously with decrease in temperature, the amount of protein reflects the mRNA levels during later times but not the initial time of exposure to cold.

Adipose Tissue, Brown↗