Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have analysed the pattern of expression of the hexokinase isoenzyme group in RIN-m5F insulinoma cells. Three hexokinase forms were resolved by DEAE-cellulose chromatography. The most abundant isoenzyme co-eluted with hexokinase type II from rat adipose tissue and displayed a Km for glucose of 0.15 mM, similar to the adipose-tissue enzyme. Hexokinase type II was in large part associated with a particulate subcellular fraction in RIN-m5F cells. The two other hexokinases separated by ion-exchange chromatography were an enzyme similar to hexokinase type I from brain and glucokinase (or hexokinase type IV). The latter isoenzyme was identified as the liver-type glucokinase by the following properties: co-elution with hepatic glucokinase from DEAE-cellulose and DEAE-Sephadex; sigmoid saturation kinetics with glucose with half-maximal velocity at 5.6 mM and Hill coefficient (h) of 1.54; suppression of enzyme activity by antibodies raised against rat liver glucokinase; apparent Mr of 56,500 and pI of 5.6, as shown by immunoblotting after one- and two-dimensional gel electrophoresis; peptide map identical with that of hepatic glucokinase after proteolysis with chymotrypsin and papain. These data indicate that the gene coding for hepatic glucokinase is expressed in RIN-m5F cells, a finding consistent with indirect evidence for the presence of glucokinase in the beta-cell of the islet of Langerhans. On the other hand, the overall pattern of hexokinases is distinctly different in RIN-m5F cells and islets of Langerhans, since hexokinase type II appears to be lacking in islets. Alteration in hexokinase expression after tumoral transformation has been reported in other systems.
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PMID:Hexokinase isoenzymes of RIN-m5F insulinoma cells. Expression of glucokinase gene in insulin-producing cells. 303 55

An islet cell tumor, characterized by proinsulin level significantly elevated above normal human pancreas, has been found to contain insulin- and glucagon-degrading activity. Examination by chromatography on Sephadex G-75 of the degradation products formed from insulin showed A chain, and B chain rich-A chain aggregate as previously found with rat pancreatic islets. There was, however, little conversion of A chain to low molecular weight components indicating that insulinoma peptidase that has been found to degrade glucagon at about pH 6.8 degraded that A chain to a markedly lower rate. In contrast to the insulin-degrading activity, which was activated by glutathione in the presence of EDTA, the peptidase activity was not affected by the thiol compound. The activity of the peptidase was markedly inhibited by chelating agents, i.e., EDTA and o-phenanthroline, whereas chymotrypsin and trypsin inhibitors, i.e., TOS-PheCH2Cl, TOS-LysCH2Cl, soybean and pancreas trypsin inhibitor were found to have no effect.
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PMID:Thiol-protein disulfide oxidoreductase and peptidase activities in insulinoma tissue. 632 44

Coenzyme Q(0) (Q(0)), a strong electrophile, is toxic to insulin-producing cells. Q(0) was incubated with rat and human pancreatic islets and INS-1 insulinoma cells, and its attachment to cellular proteins was studied with Western analysis using antiserum raised against the benzoquinone ring structure of ubiquinone (anti-Q). Q(0) covalently bonded to two proteins, one of 50 kDa and another of 70 kDa. Both proteins were found to be mitochondrial in human and rat islet cells and in many rat organs. Mitochondria were incubated with Q(0), and affinity-purified anti-Q was used to immunoprecipitate the 50-kDa protein. Amino acid sequencing identified it as dihydrolipoamide succinyltransferase, the E2 component of the alpha-ketoglutarate dehydrogenase complex (KDC). Western analysis also showed that Q bonds to the E2 components of the purified KDC and (0)the pyruvate dehydrogenase complex (PDC). Dihydrolipoamide acetyltransferase, the E2 of the PDC, has a molecular mass of 70 kDa, and the 70-kDa protein was inferred to be this enzyme. Q(0) was found to bond only to proteins containing dihydrolipoate, and in preparations of mitochondria, thiol reducing agents facilitated the attachment of Q(0), but oxidizing agents prevented it, suggesting that Q(0) bonds to thiols of dihydrolipoamide. Incubation of human or pig PDC with Q(0) followed by matrix-assisted laser desorption ionization time-of-flight and liquid chromatography/electrospray ionization mass spectrometry analyses of chymotrypsin-digested peptides of PDC E2 confirmed that Q(0) bonds to the dihydrolipoamide in these proteins. In mitochondria, coenzymes Q(1) and Q(2) did not bond to the 50-kDa protein but competed with the bonding of Q(0) to this protein. The prevention by Q(1) of characteristics the bonding of Q(0) to KDC E2, as well as other of the Q(0) effect, are reminiscent of the action of Q(0) on the mitochondrial permeability transition pore described previously (Fontaine, E., Ichas, F., and Bernardi, P. (1998) J. Biol. Chem. 273, 25734-25740).
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PMID:Immunochemical identification of coenzyme Q0-dihydrolipoamide adducts in the E2 components of the alpha-ketoglutarate and pyruvate dehydrogenase complexes partially explains the cellular toxicity of coenzyme Q0. 1507 42