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Jen-Jen Lin Tzung-Horng Yang Benjamin D. Wahlstrand Peter A. Fields George N. Somero 《Journal of molecular evolution》2002,54(1):107-117
Unlike birds and mammals, teleost fish express two paralogous isoforms (paralogues) of cytosolic malate dehydrogenase (cMDH;
EC 1.1.1.37; NAD+: malate oxidoreductase) whose evolutionary relationships to the single cMDH of tetrapods are unknown. We sequenced complementary
DNAs for both cMDHs and the mitochondrial isoform (mMDH) of the fish Sphyraena idiastes (south temperate barracuda) and compared the sequences, kinetic properties, and thermal stabilities of the three isoforms
with those of mammalian orthologues. Both fish cMDHs comprise 333 residues and have subunit masses of approximately 36 kDa.
One cytosolic isoform, cMDH-S, was significantly more heat-stable than either the other cMDH (cMDH-L) or mMDH. In contradiction
to the generally accepted model of vertebrate cMDH evolution, our phylogenetic analysis indicates that the duplication of
the fish cytosolic paralogues occurred after the divergence of the lineages leading to teleosts and tetrapods. cMDH-L and
cMDH-S differed in optimal concentrations of substrates and cofactors and apparent Michaelis–Menten constants, suggesting
that the two paralogues may play distinct physiological roles. Differences in intrinsic thermal stability among MDH paralogues
may reflect different degrees of stabilization in vivo by extrinsic stabilizers, notably protein concentration in the case
of mMDH. Thermal stabilities of porcine mMDH and cMDH-L, but not cMDH-S, were significantly increased when denaturation was
measured at a high protein (bovine serum albumin; BSA) concentration, but the BSA-induced stabilization reduced the catalytic
activity.
Received: 5 April 2001 / Accepted: 28 June 2001 相似文献
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Jen-Jen Lin Jeffrey D. Meyer John F. Carpenter Mark Cornell Manning 《International journal of biological macromolecules》2009,45(2):91-96
A terminal pasteurization step has been used for some plasma-derived protein products such as human serum albumin (HSA), which consists of heating the protein in solution at 60 °C for 10 h. Native and denaturing SDS-PAGE and dynamic light scattering were used to follow the stability of HSA during this process. It appears that a thermally unstable fraction, comprised primarily of haptoglobin, is involved in the formation of soluble aggregates of HSA. Therefore, it appears that aggregation during heat treatment is not due to conformational instability of HSA itself, but arises from unfolding of a thermally labile protein impurity. As haptoglobin aggregates, it entraps some HSA, which is present at much higher concentrations. This study emphasizes that, in a complex mixture of naturally occurring proteins, one thermally labile species can trigger aggregation of more stable proteins. 相似文献
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