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At least 523 records · Page 29Linked to original sources
PubMed2006

Macrophage migration inhibitory factor: isolation from bovine brain.

The purification of macrophage migration inhibitory factor (MIF) from bovine brain cytosol and its partial characterization are reported. A rapid and relatively simple method for MIF isolation was developed based mainly on size-exclusion chromatography on Toyopearl TSK polymer having a tendency to adsorb MIF as compared to elution of other proteins with similar molecular weights. The method gives a high yield of MIF (0.1 mg homogenous protein per g wet tissue). The retardation is conveniently utilized to achieve good separations of MIF from other proteins of similar molecular weights. The isolated protein was identified as MIF by SDS-electrophoresis, immunoblotting, sequencing of the N-terminal amino acid residues, and also by determination of keto-enol tautomerase activity that is characteristic of MIF with p-hydroxyphenylpyruvic acid as a substrate.

Animals↗
PubMed1995

Crystal structure of human alpha-thrombin complexed with hirugen and p-amidinophenylpyruvate at 1.6 A resolution.

Crystals of human alpha-thrombin complexed with hirugen and the alpha-keto acid thrombin inhibitor APPA (p-amidinophenylpyruvate) that diffract to 1.6 A resolution were obtained by soaking an alpha-thrombin-hirugen crystal in a solution of APPA. The crystal structure was determined using the difference Fourier method and refined to an R factor of 18.7% at 1.6 A resolution. This structure is the highest resolution structure of the thrombin molecule that is currently available. With the exception of the region near Arg77A-Asn78, the structures of the thrombin and hirugen molecules in the ternary complex are similar to those reported for the thrombin-hirugen binary complex. As previously determined for the APPA-trypsin complex, the carbonyl carbon atom of APPA forms a covalent bond with O gamma of Ser195 of thrombin to yield a "transition-state" analog of the tetrahedral intermediate. Comparison of the specificity pocket of the APPA complexes of thrombin and trypsin reveals differences in hydrogen bonding and shows for the first time that the S1 site of thrombin is larger than that of trypsin and as a result thrombin may be able to accommodate a bulkier P1 group than trypsin.

Amino Acid Sequence↗
PubMed1973

The use of ternary complexes to study ionizations and isomerizations during catalysis by lactate dehydrogenase.

1. The binding of oxamate to pig heart and pig muscle isoenzymes of lactate dehydrogenase in the presence of NADH was studied by fluorescence titration. The dissociation constant of oxamate from the heart enzyme complex is 3mum and from the muscle isoenzyme 25mum at pH5. These values quantitatively increase with pH as predicted if oxamate can bind only to the enzyme-NADH complex if a group with pK6.9 is protonated. There are four non-interacting oxamate-binding sites per tetramer. 2. o-Nitrophenylpyruvate is a poor substrate for both isoenzymes but has a reasonable affinity to the heart isoenzyme. Initially, it forms an enzyme-NADH-substrate complex, which can be detected either by protein-fluorescence quenching or by NADH-fluorescence quenching. The pH-dependence of the dissociation constant of nitrophenylpyruvate also shows that this ternary complex can only form if a group with pK6.8 is protonated. Taken with the results of chemical-modification experiments, these results allow the pK of 6.8 to be assigned to a system probably involving the imidazole side chain of histidine-195. Formation of a ternary complex from a binary one at pH8 is predicted to result in a proton being taken up from solution. 3. Isotope-effect studies with NADH and its deuterium analogue show that the rapidly formed ternary complex with o-nitrophenylpyruvate slowly isomerizes to give an active ternary complex, which then rapidly decomposes to NAD(+). The isomerization is pH-independent, and it is suggested that histidine-195 is still protonated in the activated ternary complex, which is present before hydride transfer. 4. All four subunits of the enzyme are kinetically equivalent with respect to the oxidation of bound NADH by o-nitrophenylpyruvate. 5. A partial mechanism for the enzyme is described which emphasizes the isomerizations and ionizations involved in forming the reduced ternary complex at pH6 and 8.

Amino Acids↗
PubMed1975

The Sulphation of p-hydroxyphenylpyruvic acid and related compounds by the rat liver cytosol.

Cytosol preparations of rat liver and kidney were examined for their ability to transfer sulphate from adenosine 3'-phosphate 5'-sulphatophosphate to p-hydroxyphenylpyruvic acid. Little activity towards this substrate was observed, and the main product detected in the reaction mixtures was identified as p-hydroxybenzyl alcohol O-sulphate. This was not formed from p-hydroxybenzaldehyde, a spontaneous oxidation product of p-hydroxyphenylpyruvic acid, by sulphation followed by a rapid enzyme-catalysed reduction of the intermediate phydroxybenzaldehyde O-sulphate. This product was formed mainly by this sequence of reactions, but the reverse, reduction followed by sulphation, also appeared possible. p-Hydroxybenzyl alcohol itself was very readily sulphated by both preparations, and the liver also produced a sulpho-conjugate of homogentisic acid. These observations are important in calculating the turnover of L-tyrosine O-sulphate in the mammalian system, and establish that p-hydroxyphenylpyruvic acid O-sulphate is an end product of its metabolism, rather than an intermediate in its synthesis by reversed transamination.

Animals↗
PubMed2006

Fungal metabolic model for tyrosinemia type 3: molecular characterization of a gene encoding a 4-hydroxy-phenyl pyruvate dioxygenase from Aspergillus nidulans.

Mutations in the human HPD gene (encoding 4-hydroxyphenylpyruvic acid dioxygenase) cause hereditary tyrosinemia type 3 (HT3). We deleted the Aspergillus nidulans homologue (hpdA). We showed that the mutant strain is not able to grow in the presence of phenylalanine and that it accumulates increased concentrations of tyrosine and 4-hydroxyphenylpyruvic acid, mimicking the human HT3 phenotype.

4-Hydroxyphenylpyruvate Dioxygenase↗