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H Gehring

Publications and source records attributed to H Gehring.

At least 91 records · Page 5Linked to original sources
PubMed1982

Biosynthesis of aspartate aminotransferases. Both the higher molecular weight precursor of mitochondrial aspartate aminotransferase and the cytosolic isoenzyme are synthesized on free polysomes.

The site of synthesis of the higher molecular weight precursor of mitochondrial aspartate aminotransferase (Sonderegger, P., Jaussi, R., and Christen, P. (1980) Biochem. Biophys. Res. Commun. 94, 1256-1260) has been determined by separation of free and membrane-bound polysomes under ionic conditions imitating the intracellular milieu and in vitro read-out translation of the two polysome fractions in a rabbit reticulocyte lysate. The amounts of the precursor of mitochondrial aspartate aminotransferase synthesized by free and membrane-bound polysomes were compared with the relative extent of the synthesized of cytosolic aspartate aminotransferase in the same fractions. Only a small (less than 10% of total) and for both isoenzymes quantitatively equivalent fraction was found to be produced by the membrane-bound polysome fraction; very likely, it has to be attributed to contaminating free polysomes. Apparently, the import of mitochondrial aspartate aminotransferase into the mitochondria does not involve an association of polysomes with intracellular membranes.

Animals↗
PubMed1980

Structure and function of carboxypeptidase A alpha in supercooled water.

The spectral and enzymatic characteristics of chromophoric derivatives of carboxypeptidase A alpha (EC 3.4.17.1) have been examined at subzero temperatures in supercooled water-in-oil emulsions. Substrate and temperature dependencies of enzyme kinetics indicated the existence of a solution-like enzyme phase that greatly extends the temperature range (greater than 60 degrees C) over which the activity of this enzyme can be measured. The emulsion spectra were virtually identical to those of solutions over a wide range of temperatures. Subzero temperatures (less than -10 degrees C) may induce changes of enzyme conformation but not of geometry at the site of the metal atom, nor do they adversely affect activity at any of the temperatures studied. Both structure and function of carboxypeptidase A alpha can be examined in supercooled water under identical reaction conditions.

Carboxypeptidases↗
PubMed1977

Active-site labeling of aspartate aminotransferases by the beta,gamma-unsaturated amino acid vinylglycine.

The pyridoxal form of both cytosolic and mitochondrial aspartate aminotransferase is irreversibly inactivated consequent to its interaction with the beta,gamma-unsaturated substrate analogue vinylglycine. Per catalytic cycle, 90% of the enzyme molecules are inactivated while 10% escape inactivation by transamination to the pyridoxamine form. In the presence of vinylglycine plus 2-oxoglutarate, inactivation is complete because of retransamination of the pyridoxamine form to the susceptible pyridoxal form. Peptide analyses after inactivation with [1-14C]vinylglycine showed that vinylglycine alkylates the active-site lysine residue 258 which forms the internal aldimine with the coenzyme pyridoxal 5'-phosphate. The coenzyme itself is left intact; resolution of the inactivated enzyme by base or trichloroacetic acid yields pyridoxal-5'-P. The absorption spectrum of the inactivated enzyme (lambdamax 335 nm) suggests that the cofactor is bound as a substituted aldimine. The proposed pathway of alkylation of Lys-258 involves abstraction of the alpha proton from vinylglycine, isomerization to the alpha,beta-unsaturated enamine, and subsequent nucleophilic attack of the epsilon-amino group of the lysyl residue at the beta carbon of the inhibitor. The determination of the amino acid sequence around the coenzyme-binding lysyl residue in the mitochondrial isoenzyme from chicken gave Ala-(epsilon-Pxy)Lys-Asn-Met-(Gly,Leu,Tyr) which is identical with the other mitochondrial transaminases examined so far.

Amino Acid Sequence↗
PubMed1977

Interspecies comparison of cytosolic and mitochondrial aspartate aminotransferases. Evidence for a more conservative evolution of the mitochondrial isoenzyme.

The degree of structural similarity between the mitochondrial isoenzymes of aspartate aminotransferase from pig heart and chicken heart was determined by means of their immunological cross-reactivity and compared with the degree of similarity between the cytosolic isoenzymes from the same two species. Quantitative microcomplement fixation revealed a remarkable similarity of the two mitochondrial isoenzymes corresponding to an immunological distance of 104. The structures of the two cytosolic isoenzymes, on the other hand, diverge with an immunological distance of 203. The apparent conservatism of mitochondrial aspartate aminotransferase indicates additional evolutionary constraints on the structure of this organelle-confined isoenzyme.

Animals↗
PubMed1972

[Elephant pox].

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Animals↗