Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inheritance of mitochondrial DNA (mtDNA) in Saccharomyces cerevisiae is usually biparental. Pedigree studies of zygotic first buds indicate limited mixing of wild-type (p+) parental mtDNAs: end buds are frequently homoplasmic for one parental mtDNA, while heteroplasmic and recombinant progeny usually arise from medial buds. In crosses involving certain petites, however, mitochondrial inheritance can be uniparental. In this study we show that mitochondrial sorting can be influenced by the parental mtDNAs and have identified intermediates in the process. In crosses where mtDNA mixing is limited and one parent is prelabeled with the matrix enzyme citrate synthase 1 (CS1), the protein freely equilibrates throughout the zygote before the first bud has matured. Furthermore, if one parent is p0 (lacking mtDNA), mtDNA from the p+ parent can also equilibrate; intracellular movement of mtDNA is unhindered in this case. Surprisingly, in zygotes from a p0 CS1+ x p+ CS1- cross, CS1 is quantitatively translocated to the p+ end of the zygote before mtDNA movement; subsequently, both components equilibrate throughout the cell. This initial vectorial transfer does not require respiratory function in the p+ parent, although it does not occur if that parent is p-. Mouse dihydrofolate reductase (DHFR) present in the mitochondrial matrix can also be vectorially translocated, indicating that the process is general. Our data suggest that in zygotes mtDNA movement may be separately controlled from the movement of bulk matrix constituents.
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PMID:Patterns of mitochondrial sorting in yeast zygotes. 844 7

Ligand-induced conformational changes of GroEL alone and with bound rhodanese, citrate synthase, or dihydrofolate reductase were studied by limited proteolysis. Similar digestion patterns of GroEL, with or without bound substrate polypeptide, were obtained in the absence and presence of the chaperonin ligands, K+, Mg2+, or ATP. The rates of formation and degradation of the six produced proteolytic fragments were significantly different, however. Strikingly, only with Mg2+/ATP or K+/Mg2+/ATP an additional fragment of approximately 25 kDa was generated during digestion of GroEL alone or with bound rhodanese or dihydrofolate reductase, but not with bound citrate synthase. Most of the trypsin-sensitive sites in GroEL were localized in the flexible apical domain, which contains the putative polypeptide-binding region. Our data indicate that subtle structural changes in the trypsin-sensitive regions of GroEL occur as a result of the binding of the chaperonin ligands. However, these structural changes are influenced by the GroEL substrate polypeptides.
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PMID:Ligand-induced conformational changes of GroEL are dependent on the bound substrate polypeptide. 866 87

Recent simulation work has indicated that channeling of charged substrates between the active sites of bifunctional enzymes or bienzyme complexes can be significantly enhanced by favorable interactions with the electrostatic field of the enzymes. The results of such simulations are expressed in terms of transfer efficiencies, which describe the probability that substrate leaving the active site of the first enzyme will reach the active site of the second enzyme before escaping out into bulk solution. The experimental indicators of channeling, on the other hand, are factors such as a decrease in the transient (lag) time for appearance of the final product of the coupled enzyme reaction or a decrease in the susceptibility of the overall reaction rate to the presence of competing enzymes or competitive inhibitors. The work reported here aims to establish a connection between the transfer efficiencies obtained from simulation, with the above-mentioned experimental observables. This is accomplished by extending previously reported analytical approaches to combine the simulated transfer efficiency with the Michaelis-Menten kinetic parameters Km and Vmax of the enzymes involved; expressions are derived to allow both transient times and steady state rates to be calculated. These results are applied to the two systems that have been studied both theoretically and experimentally. In the first case, that of the bifunctional enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS), the experimentally observed decrease in transient times is found to be consistent with a transfer efficiency of >/=80%. In the second case, that of a citrate synthase-malate dehydrogenase fusion protein, a transfer efficiency of 73% is consistent with the experimental transient time measurements. Separate and independent analysis of the effects of adding the competing enzyme aspartate aminotransferase gives a transfer efficiency of 69%, in excellent agreement with the transient time results. The transfer efficiencies thus obtained from experimental results are in both cases in good agreement with those obtained from simulations that include electrostatic interactions. One important discrepancy between simulation and experiment, is however, found in the reported effects of adding a competitive inhibitor in the DHFR-TS system: qualitatively different results are expected from the theoretical analysis. A possible reason for this apparent contradiction is discussed.
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PMID:Electrostatic channeling of substrates between enzyme active sites: comparison of simulation and experiment. 940 38