PubMed Health⌕ Search

Biomedical subjects

K B Freeman

Publications and source records attributed to K B Freeman.

At least 55 records · Page 3Linked to original sources
PubMed1980

Hydrophobic interaction between the monomer of mitochondrial malate dehydrogenase and phospholipid membranes.

Porcine mitochondrial malate dehydrogenase (EC 1.1.1.37) dissociates into subunits on dilution. The enzyme monomer caused large increases in the surface pressure of monolayers of 1:1 phosphatidylserine/phosphatidylcholine at air/water and oil/water interfaces. The monomer increased the permeability of phospholipid vesicles to 22Na+. Both effects were significantly greater than the corresponding effects of ribonuclease A, cytochrome c and the dimeric form of malate dehydrogenase. Changes in the circular-dichroism spectra of the enzyme indicated that conformational changes may be associated with dimer formation or when monomer interacts with lysophosphatidyl-choline. Similar interactions to those described may occur in situ when mitochondrial malate dehydrogenase is transported to the mitochondrial matrix from its site of synthesis on cytosolic ribosomes.

Animals↗
PubMed1979

Interaction of mitochondrial malate dehydrogenase monomer with phospholipid vesicles.

The association between bovine and porcine mitochondrial malate dehydrogenase (EC 1.1.1.37) and phospholipid vesicles was investigated. At concentrations at which malate dehydrogenase exists as a dimer, entrapment within the aqueous compartment but not binding of the 14C-labelled enzyme was observed. The dissociated enzyme was labile to moderate heat and to p-chloromercuribenzoate, but in both cases inactivation was decreased by incubation with suspensions of charged phospholipid vesicles. This suggested an interaction between enzyme subunits and phospholipid, and this was confirmed by direct binding measurements and by studies that followed changes in the fluorescein-labelled enzyme. The circular-dichroism spectra of the enzyme indicated a high alpha-helix content, and suggested that a small conformational change occurred when the enzyme dissociated. Fluorescence data also suggested less-rigid molecules after dissociation. A possible mechanism, based on the flexibility of enzyme monomer and its interaction with phospholipids, by which mitochondrial matrix enzymes are specifically localized in cells, is discussed.

Animals↗
PubMed1979

Mitochondrial malic enzyme in mosaic skeletal muscle of mouse chimeras.

The question was investigated whether mitochondria in the mammalian skeletal muscle fiber syncytium incorporate gene products encoded by one or many nuclei. Mouse chimeras were produced from strains which differ in their electrophoretic variants of the nuclear-coded mitochondrial protein, malic enzyme (MOD-2, E.C. 1.1.1.40, L-malate NADP+ oxidoreductase decarboxylating). The MOD-2 phenotypes of skeletal muscles of these chimeras were characterized in a starch gel electrophoretic system. The results indicate that individual mitochondria can contain products encoded by multiple nuclei and therefore that, for skeletal muscle mitochondria, the cell is not subdivided into nuclear territories. Possible mechanisms of gene product distribution in skeletal muscle fibers are discussed.

Animals↗
PubMed1979

Mammalian mitochondrial transfer RNAs: chromatographic properties, size and origin.

Incubation of isolated rat liver mitochondria with radioactive amino acids resulted in the charging of tRNAs for arginine, asparagine, leucine, lysine, methionine, proline and valine. The aminoacyl-tRNAs were shown to be distinct from their cytosolic counterparts by chromatography on RPC-5. By electrophoresis on urea polyacrylamide slab gels it was found that all these mitochondrial aminoacyl-tRNAs were about 70-76 nucleotides long. The unique mitochondrial asparaginyl- and prolyl-tRNAs, not previously identified in mammalian cells, were shown to hybridize to mtDNA. Mitochondrial leucyl-tRNA separated into 3 peaks on RPC-5 and the first species was shown to be different than a combination of the other two by molecular size and partial RNase T1 digestion patterns. Each was coded by a separate gene on mtDNA as shown by partial additivity of hybridization. Separate genes for mitochondrial tRNAMetm and tRNAMetf, separated by RPC-5 chromatography, were also demonstrated. These results bring to 21 the number of individual tRNAs coded by mammalian mtDNA.

Animals↗
PubMed1979

Binding of mitochondrial malate dehydrogenase to mitoplasts.

The binding of 14C-labelled bovine and porcine malate dehydrogenase (EC 1.1.1.37) to rat liver mitochondria and mitoplasts was examined. The bovine enzyme was found to associate nonspecifically with isolated mitochondria and sonicated mitoplasts. Scatchard plot analysis suggested a specific binding to mitoplasts of the order of 5 pmol malate dehydrogenase per milligram of mitoplast protein. Porcine malate dehydrogenase dimer but not monomer exhibited a similar binding. The results are discussed in relation to the mechanism of uptake of the enzyme by mitochondria after synthesis on cytosolic ribosomes.

Animals↗
PubMed1978

Chemical and physical properties of mammalian mitochondrial aminoacyl-transfer RNAs. I. Molecular weights of mitochondrial leucyl- and methionyl-transfer RNAs.

The sedimentation and electrophoretic properties of Syrian hamster cytosolix and mitochondrial methionyl- and leucyl- +RNAs have been compared under denaturing conditions. Mitochondrial leucyl-tRNA could be separated into three species by chromatography on RPC-5. Their apparent molecule weights as determined by polyacrylamide slab gel elecltrophoresis were 23 000 for one species and 24 000 for the other two compared to the five cytosolic leucyl-tRNA species whose apparent molecular weights ranged from 26 000 to 28 000. Mitochondrial leucyl-tRNAs sedimented more slowly than their cytosolic counterparts, again indicating a lower molecular weight. The apparent molecular weights of the mitochondrial methionyl-tRNAs were identical or only slightly lower than their cytosolic counterparts as determined by polyacrylamide slab gel electrophoresis but both mitochondrial methionyl-tRNA and formylmethionyl-tRNA sedimented slightly more slowly than cytolsolic methionyl-tRNA. It is suggested that mitochondrial tRNAs fall into the size range of other t RNAs and might be uniform in size.

Animals↗
PubMed1978

Chemical and physical properties of mammalian mitochondrial aminoacyl-transfer RNAs. II. Analysis of 7-methylguanosine in mitochondrial and cytosolic aminoacyl-transfer RNAs.

The 7-methylguanosine (m7G) content of two individual mitochondrial tRNAs, labelled in the aminoacyl moiety was assayed by the specific cleavage of the tRNA at this nucleotide followed by electrophoretic analysis to identify the 3'-terminal fragment of the tRNA. Neither Syriam hamster mitochondrial tRNALeu nor tRNAMet were found to contain m7G. In contrast, cytosolic tRNAMetS were cleaved indicating the presence of m7G, apparently 27--28 and 29 nucleotides from their 3' terminus. Cystolic tRNALeu was not cleaved. These results are discussed in relationship to the reported low content of methylated nucleosides in mitochondrial 4 S RNA.

Animals↗
PubMed1978

Conservation of genes coding for proteins synthesized in human mitochondria.

Proteins synthesized in mitochondria of 27 different human cell lines, identified by labeling with [35S]methionine in the presence of cycloheximide, have been enumerated and their electrophoretic mobilities determined by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis and fluorography. Twelve bands were observed in all cell lines. In 24 cell lines, the electrophoretic mobilities of the proteins were the same regardless of race, sex, tissue of origin, cell type, viral transformation, or premature biological aging syndromes. The patterns obtained for the remaining cell lines, HeLa, KB, and Hep-2 were identical. These cell lines showed one protein component that was absent in the 24 others, and lacked a component present in these cell lines. Since it has been previously asserted that KB and Hep-2 are HeLa cells, the data indicate that one basic pattern exists in human cells with a variant of unknown origin occurring in HeLa cells.

Cell Line↗
PubMed1978

Biochemical and genetic approaches to the study of mammalian mitochondrial tRNAs.

The possible existence of mammalian mitochondrial asparaginyl-tRNA has been examined using a variety of approaches. [3H]Asparagine was incorporated into protein by mitochondria of the Chinese hamster ovary (CHO) cell line Asn-7, which has a temperature-sensitive cytosolic asparaginyl-tRNA synthetase, either in the presence of cycloheximide or at a nonpermissive temperature. Isolated mitochondria of CHO thymidine kinase minus (TK-) cells also incorporated the amino acid into protein. In each case, the number and electrophoretic mobility of the proteins was the same as mitochondrially synthesized proteins of CHO TK- cells labelled with [35S]methionine. A tRNAAsn could be charged in isolated CHO TK- cell mitochondria and the asparaginyl-tRNA was found to elute before its cytosolic counterpart on an RPC-5 column and to have a higher mobility on polyacrylamide slab gels run under denaturing conditions. This is the first demonstration of a unique mitochondrial asparaginyl-tRNA.

Asparagine↗
PubMed1978

Interspecific variations in proteins synthesized by mammalian mitochondria.

The products of mitochondrial protein synthesis in established cell lines of various mammalian species were labelled with [35S]methionine and their number and apparent molecular weights determined by sodium dodecyl sulfate polyacrylamide slab gel electrophoresis and fluorography. Proteins synthesized by isolated rat liver mitochondria were labelled with [3H]valine and similarly characterized. Each species had a distinctive pattern of from 10 to 13 mitochondrially synthesized proteins with apparent molecular weights between 10,000 and 50,000. No differences were detected in the number or electrophoretic mobility of the mitochondrially synthesized proteins of SV-40-transformed and nontransformed WI-38 cells.

Animals↗
PubMed1977

Action of the N-trifluoroacetyl analogue of D-chloramphenicol.

The N-trifluoroacetyl analogue of chloramphenicol was found to inhibit the growth of Escherichia coli less than chloramphenicol, rather than more as previously reported by others. It also inhibits protein synthesis by E. coli and rat liver mitochondria less.

Animals↗
PubMed1977

Discrete electrophoretic products of mitochondrial protein synthesis in the Chinese hamster ovary cell line.

Mitochondrial proteins labelled with [35S]methionine for 1 h in whole Chinese hamster ovary (CHO) cells in the presence of cycloheximide or emetine, known inhibitors of cytosolic protein synthesis, have been enumerated and characterized by their electrophoretic mobility in sodium dodecyl sulfate slab gel electrophoresis. Ten distinct electrophoretic bands were observed. The components were relatively stable during a 2 h postlabelling period. The same 10 bands were also seen with the CHO cell line tsH1, labelled at 40 degrees C, a temperature at which cytosolic but not mitochondrial protein synthesis is inhibited in this cell line, and with isolated mitochondria labelled in the presence of cycloheximide. An 11th band was present when [3H]leucine but not [35S]methionine was used for labelling. The width of the major band suggested that it consists of two components making a total of at least 12 proteins synthesized in mitochondria. The molecular weights of these mitochondrial proteins ranged from 5000 to 50 000 and there was a sixfold difference in the relative molar amounts synthesized in a 1-h period in the presence of [3H]leucine or [35S]methionine. No differences in number or electrophoretic mobility of the mitochondrially synthesized proteins were found among the seven CHO cell lines examined. These results suggest the stability of the mitochondrial genome in the CHO cell line.

Cell Line↗
PubMed1976

The synthesis of polyadenylic acid-containing ribonucleic acid by isolated mitochondria from Ehrlich ascites cells.

The synthesis of poly(A)-containing RNA by isolated mitochondria from Ehrlich ascites cells was studied. Isolated mitochondria incorporate [3H]AMP or [3H]UTP into an RNA species that adsorbs on oligo (dT)-cellulose columns or Millipore filters. Hydrolysis of the poly(A)-containing RNA with pancreatic and T1 ribonucleases released a poly(A) sequence that had an electrophoretic mobility slightly faster than 4SE. In comparison, ascites-cell cytosolic poly(A)-containing RNA had a poly(A) tail that had an electrophoretic mobility of about 7SE. Sensitivity of the incorporation of [3H]AMP into poly(A)-containing RNA to ethidium bromide and to atractyloside and lack of sensitivity to immobilized ribonuclease added to the mitochondria after incubation indicated that the site of incorporation was mitochondrial. The poly(A)-containing RNA sedimented with a peak of about 18S, with much material of higher s value. After denaturation at 70 degrees C for 5 min the poly(A)-containing RNA separated into two components of 12S and 16S on a 5-20% (w/v) sucrose density gradient at 4 degrees C, or at 4 degrees and 25 degrees C in the presence of formaldehyde. Poly(A)-containing RNA synthesized in the presence of ethidium bromide sedimented at 5-10S in a 15-33% (w/v) sucrose density gradient at 24 degrees C. The poly(A) tail of this RNA was smaller than that synthesized in the absence of ethidium bromide. The size of the poly(A)-containing RNA (approx. 1300 nucleotides) is about the length necessary for that of mRNA species for the products of mitochondrial protein synthesis observed by ourselves and others.

Adenosine Monophosphate↗