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At least 1,711 records · Page 95Linked to original sources
PubMed1979

Assembly of the mitochondrial membrane system: sequences of yeast mitochondrial valine and an unusual threonine tRNA gene.

The mitochondrial DNA segments of two independently isolated rho- clones of S. cerevisiae carrying a genetic marker for a threonine tRNA have been characterized by restriction endonuclease analysis and DNA sequencing. The DNA sequences of the two segments have been used to deduce the primary and secondary structures of the tRNA. The threonine tRNA is unusual in having a leucine anticodon (3'-GAU-5'). Despite the anomalous anticodon, the tRNA is proposed to function in mitochondrial protein synthesis. One of the rho- clones contains an additional coding sequence that has been identified as a valine tRNA genes have been located on the wild-type physical map and determined to be transcribed from two different strands.

Base Sequence↗
PubMed1989

MOM19, an import receptor for mitochondrial precursor proteins.

We have identified a 19 kd protein of the mitochondrial outer membrane (MOM19). Monospecific IgG and Fab fragments directed against MOM19 inhibit import of precursor proteins destined for the various mitochondrial subcompartments, including porin, cytochrome c1, Fe/S protein, F0 ATPase subunit 9, and F1 ATPase subunit beta. Inhibition occurs at the level of high affinity binding of precursors to mitochondria. Consistent with previous functional studies that suggested the existence of distinct import sites for ADP/ATP carrier and cytochrome c, we find that import of those precursors is not inhibited. We conclude that MOM19 is identical to, or closely associated with, a specific mitochondrial import receptor.

Animals↗
PubMed1990

Early steps in mitochondrial protein import: receptor functions can be substituted by the membrane insertion activity of apocytochrome c.

The process of insertion of precursor proteins into mitochondrial membranes was investigated using a hybrid protein (pSc1-c) that contains dual targeting information and, at the same time, membrane insertion activity. pSc1-c is composed of the matrix-targeting domain of the cytochrome c1 presequence joined to the amino terminus of apocytochrome c. It can be selectively imported along either a cytochrome c1 route into the mitochondrial matrix or via the cytochrome c route into the intermembrane space. In contrast to cytochrome c1, pSc1-c does not require the receptor system/GIP for entry into the matrix. The apocytochrome c in the pSc1-c fusion protein appears to exert its membrane insertion activity in such a manner that the matrix-targeting sequence gains direct access to the membrane potential-dependent step. These results attribute an essential function to the receptor system in facilitating the initial insertion of precursors into the mitochondrial membranes.

Adenosine Triphosphate↗
PubMed1982

Ca2+ transporting activity of membrane fractions isolated from the post-mitochondrial supernatant of rat liver.

The post-mitochondrial supernatant of rat liver contains two vesicular fractions which transport Ca2+ actively. The heavier fraction, sedimenting at 17.500 xg, 20 min, is enriched in plasma membrane markers and apparently contains both a Ca2+ pumping ATPase and a Na+/Ca2+ exchanger. These activities have been attributed to the plasma membrane vesicles. The lighter fraction, sedimenting at 100.000 xg, 60 min, is enriched in endoplasmic reticulum markers, and contains only a Ca2+ pumping ATPase, which can be differentiated from that of the heavier fraction on the basis of the sensitivity to vanadate. The Ca2+ pumping activity of endoplasmic reticulum appears to be regulated by both a cAMP-dependent, and a calmodulin-dependent system. The former system involves a heat-stable protein fraction from the cytosol. The regulation by the cAMP and the calmodulin-dependent systems involves the phosphorylation of several proteins in the endoplasmic reticulum membrane.

Animals↗
PubMed1985

Intramitochondrial localization of fumarate reductase, NADPH----NAD transhydrogenase, 'malic' enzyme and fumarase in adult Hymenolepis diminuta.

The intramitochondrial localization of the fumarate reductase, NADPH----NAD transhydrogenase, 'malic' enzyme and fumarase was determined in adult Hymenolepis diminuta. The distribution of marker enzymes for the inner membrane, matrix, intermembrane space and outer membrane of H. diminuta mitochondria simulated that of the corresponding ascarid and mammalian organelles. The electron transport-coupled fumarate reductase and the NADPH----NAD transhydrogenase were components of the inner membrane whereas the 'malic' enzyme and fumarase were in the matrix soluble compartment. Assessments of NADH utilization, malate-dependent NADP reduction and NADPH----NAD transhydrogenation by presumedly intact and disrupted mitochondria supported the localization data. The findings presented indicate that in H. diminuta mitochondria (a) NADPH and fumarate are accumulated within the matrix compartment; (b) transhydrogenation between NADPH and NAD is an event associated with the matrix side of the inner membrane; and (c) electron transport-dependent NADH oxidation and fumarate reduction occur at sites on the matrix side of the inner membrane.

Animals↗