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M Hui

Publications and source records attributed to M Hui.

47 records · Page 3Linked to original sources
PubMed1978

IV. Covalent coupling of rat liver phenylalanine hydroxylase.

Rat liver phenylalanine hydroxylase (PheH) was covalently coupled to AH-Sepharose 4B, CH-Sepharose 4B, alginic acid and polygalacturonic acid. The activities of the bound enzyme from the ethanol and ammonium sulfate fractions were studied under a variety of conditions. The ethanol enzyme coupled to AH-Sepharose 4B showed the best thermal stability from 20 degrees to 50 degrees after heating for 15 min. It retained more than 15% of its initial activity after storage at 25 degrees for 9 days. The covalently linked enzymes generally had a broader range of optimal activity from pH 5.8 to 7.5. The presence of a positive or negative microenvironment on the matrix had no effect on the activity of the enzyme coupled to AH- or CH-Sepharose 4B. The failure to obtain hydroxylase activity with enzyme linked to alginic acid or polygalacturonic acid was attributed to the acidic microenvironment of the matrices.

Animals↗
PubMed1977

Covalent coupling of calf brain prolidase.

Calf brain prolidase covalently bound to CNBr-Sepharose 4B, retained about 32% of the activity of the uncoupled enzyme. The free enzyme showed slightly greater stability than the bound preparation when stored at 20 degrees C or at 0 degrees C. However, in either case the free and bound enzymes were more stable at the lower temperature. Greater thermal stability was shown by the free enzyme than by the bound preparation over a temperature range of 25 degrees C-60 degrees C. The free and bound prolidase, with and without Mn+2, had maximal activity at pH 4.0. Although the bound enzyme showed a single maximum, the free preparation exhibited three pH maxima of 4.0, 9.0, and 6.5, in decreasing order of activity. The ions Ag+, Cu+, Hg+2, and Zn+2 were strongly inhibitory on the free enzyme, whereas inhibition of the bound enzyme, with the exception of Zn+2 , was less. Unlike the coupled enzyme, a stimulatory effect was obtained on the free preparation with Co+3, Mg+2, and Mn+2. Various other compounds were studied and their effects were noted.

Animals↗
PubMed1977

III. Covalent coupling of rat liver phenylalanine hydroxylase.

Optimal conditions have been determined for the coupling of rat liver phenylalanine hydroxylase (PheH) to activated CH-Sepharose-4B. When 12 mg of ligand was reacted with 100 mg of matrix, 20% of the initial enzyme activity was covalently bound along with 55% of the protein. The coupled enzyme showed greater thermal stability from 50 degrees to 60 degrees after heating for 15 min, a lower optimum pH, 5.8, slightly less inhibition by Ag+, Cu+2, and Hg+2, and greater resistance to hydrolysis by alpha-chymotrypsin and protease. The uncoupled enzyme, however, exhibited greater storage stability than the covalently linked enzyme at 25 degrees after 24 hrs and at 0 degrees after 21 days. Alteration of the microenvironment by the introduction of sulfhydryl groups and positive and negative charged carriers during coupling of the enzyme either had no effect or markedly reduced hydroxylase activity.

Animals↗
PubMed1976

Haemodialysis and copper fever.

A syndrome of headache, chills, sweating, nausea, and exhaustion during and after haemodialysis is described and likened to metal fume fever. A patient has been cured of this syndrome following removal of copper-containing parts from the water-path of her home dialysis system.

Adolescent↗
PubMedDate not supplied

Enkephalin-containing polypeptides are potent inhibitors of enkephalin degradation.

Enkephalin-containing polypeptides derived from pro-enkephalin A, pro-enkephalin B, or pro-opiomelanocortin were inhibitors of enkephalin degradation by aminoenkephalinases purified from cytosol or membranes. Of the peptides, Argo-Met-enkephalin was the most potent inhibitor for the aminoenkephalinases, with an IC50 of about 0.6 microM, it was more effective than bestatin (IC50 = 0.8-1.0 microM). This inhibition was partly due to substrate competition. Argo-Met-enkephalin was hydrolyzed by aminoenkephalinases to form Arg, Tyr, and Gly-Gly-Phe-Met in a substrate-inhibited manner. The hexapeptide also inhibited the breakdown of Arg- and Tyr-beta-naphthylamide by the membrane aminoenkephalinase. Since Argo-Met-enkephalin did not inhibit leucine aminopeptidase, it was a more selective inhibitor than bestatin of Met-enkephalin breakdown by aminopeptidases. Argo-Met-enkephalin inhibited enkephalin breakdown by synaptosomal plasma membranes but not by brain slices. Our data suggest that in addition to their possible role as opioids, the enkephalin-containing polypeptides may be regulators of enkephalin levels.

Aminopeptidases↗
PubMedDate not supplied

Changes in puromycin-sensitive aminopeptidases in postmortem schizophrenic brain regions.

We studied the distribution of puromycin-sensitive aminopeptidase (PSA) in well-defined human brain ares by Western immunoblot in an attempt to examine its possible role in schizophrenia. The schizophrenic brains were from suicide victims (n = 13) of either sex, with an age range of 30-60 yr (average 45). The controls were mostly victims of myocardial infarction (n = 12), of either sex and between 32 and 56 yr old (average 44). The brain regions were obtained within 48 h after death. After ultracentrifugation the PSA was quantified by Western blot analysis using a PSA antiserum. The distribution of the two most abundant antigens, MW 100 kDa (PSA-100) and 170 kDA (PSA-170), were compared. PSA-100 had peptidase activity, PSA-170 did not. PSA-100 was found in all of the region studied. In the control brain areas prefrontal cingulate and frontal cortices, thalamus, hippocampus, hypothalamus and outer globus pallidus contained significantly more PSA-100 than the corresponding areas from schizophrenic brain. PSA-170 was mostly found only in areas of schizophrenic brains. In three control brains, in one area of each, it could be detected, but the level in each of these regions was less than 30% of that in the corresponding schizophrenic area. PSA-170 was found in all the schizophrenic brains, in 20 of the 35 regions we studied, with parahippocampal cortex the highest (134 ng/g wet tissue) and frontal inferior cortex the lowest (9.3 ng/g wet tissue). It was not detectable in cerebral or cerebellar white matter. Our data show that the amounts and distribution of PSA-170, a protein of unknown function, is restricted mostly to schizophrenic brain areas. The difference is not due either to neuroleptic treatment of the patient or to the postmortem proteolysis of the brain samples.

Adult↗
PubMedDate not supplied

Covalent coupling of rat liver phenylalanine hydroxylase.

Optimal conditions have been determined for the coupling of rat liver phenylalanine hydroxylase (Phe H) to cyanogen bromide-Sepharose 4B. When 8 mg of ligand was reacted with 100 mg of matrix, 20 to 30 percent of the initial enzyme activity was covalently bound along with 90 percent of the protein. The coupled enzyme showed greater thermal stability from 40 degrees to 60 degrees, a broader base of optimal pH activity from 5.8 to 10.0, more resistance to proteolysis and less inhibition by various inhibitors. The uncoupled enzyme exhibited greater storage stability at 25 degrees after 24 hr and at 0 degrees after 18 days. Alteration of the microenvironment by introduction of sulfhydryl groups or of carriers having positive or negative charges had variable effects on the hydroxylase activity.

Animals↗