Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Succinyl-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide (Suc-LLVY-MCA) hydrolyzing activities of the 20S and 26S proteasomes in the gerbil cortex following transient forebrain ischemia were examined. Using extraction solutions without ATP, only 20S proteasome activity was noted after separation with glycerol gradient centrifugation. When these extracts were incubated with ATP and an ATP-regenerating system prior to glycerol gradient separation, both 20S and 26S proteasome activities were detected. Following 10 min of ischemia, the activity of the 26S proteasomes decreased, whereas the 20S proteasome activity increased after 30 min of reperfusion. These changes returned to the control level after 1 h. The active 26S proteasomes were formed with ATP-dependent association with the 20S proteasomes and several subunits and the 26S proteasomes degraded ubiquitin-protein conjugates. These results indicate that proteasome activity might not be irreversibly impaired after transient ischemia. However, transient inhibition of ATP-dependent conversion of 20S to 26S proteasomes in vitro must be one of the causes of the accumulation of the ubiquitin-protein conjugates in the early reperfusion period.
...
PMID:Changes in proteasome activity following transient ischemia. 871 10

Proteasomes are multisubunit proteases that exist universally among eukaryotes. They have multiple proteolytic activities, and are believed to have important roles in regulating cell cycle, selective intracellular proteolysis, and antigen presentation. To determine the possible role that proteasomes may play in controlling the life cycle of African trypanosomes, we have isolated proteasomes from the bloodstream and the insect (procyclic) forms of Trypanosoma brucei by DEAE-cellulose chromatography and glycerol gradient fractionation in the presence of ATP. No 26 S proteasome homologs was identified in T. brucei under these experimental conditions. The proteasomes isolated from these two forms of T. brucei are very similar to the rat blood cell 20 S proteasome in their general appearance under the electron microscope. The profile of trypanosome proteasome subunits in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) has eight visible protein bands with molecular weights ranging from 23 to 34 kDa, and cross-reacted very poorly with the anti-human 20 S proteasome antibodies on immunoblots. Two-dimensional gel electrophoresis of the parasite proteasomes shows a similar number of major subunits with pI's ranging from 4.5 to 7. Using a variety of fluorogenic peptides as substrates, the trypanosome proteasomes exhibited unusually high trypsin-like, but somewhat lower chymotrypsin-like activities, as compared to the rat 20 S proteasome. These proteolytic activities were, however, insensitive to phenylmethylsulfonyl fluoride (PMSF), tosyl-phenylalanine chloromethylketone (TPCK), tosyl-lysine chloromethylketone (TLCK) and trans-epoxy succinyl-L-leucylamido-(4 guanidino) butane (E-64), but the trypsin-like activity of trypanosome proteasomes was inhibited by leupeptin, an aldehyde known to inhibit the trypsin-like activity of mammalian proteasomes, thus ruling out possible contamination by other serine or cysteine proteases. Some quantitative differences in the substrate specificities between the proteasomes from bloodstream and procyclic forms were indicated, which may play a role in determining the differential protein turnovers at two different stages of development of T. brucei.
...
PMID:Purification and characterization of proteasomes from Trypanosoma brucei. 881 75

Nin1p, a component of the 26S proteasome of Saccharomyces cerevisiae, is required for activation of Cdc28p kinase at the G1-S-phase and G2-M boundaries. By exploiting the temperature-sensitive phenotype of the nin1-1 mutant, we have screened for genes encoding proteins with related functions to Nin1p and have cloned and characterized two new multicopy suppressors, SUN1 and SUN2, of the nin1-1 mutation. SUN1 can suppress a null nin1 mutation, whereas SUN2, an essential gene, does not. Sun1p is a 268-amino acid protein which shows strong similarity to MBP1 of Arabidopsis thaliana, a homologue of the S5a subunit of the human 26S proteasome. Sun1p binds ubiquitin-lysozyme conjugates as do S5a and MBP1. Sun2p (523 amino acids) was found to be homologous to the p58 subunit of the human 26S proteasome. cDNA encoding the p58 component was cloned. Furthermore, expression of a derivative of p58 from which the N-terminal 150 amino acids had been removed restored the function of a null allele of SUN2. During glycerol density gradient centrifugation, both Sun1p and Sun2p comigrated with the known proteasome components. These results, as well as other structural and functional studies, indicate that both Sun1p and Sun2p are components of the regulatory module of the yeast 26S proteasome.
...
PMID:Yeast counterparts of subunits S5a and p58 (S3) of the human 26S proteasome are encoded by two multicopy suppressors of nin1-1. 901 4

The aim of the present study was to characterize human CYP2E1 turnover and examine the possible proteolytic pathways responsible for the rapid degradation of CYP2E1 in a transfected HepG2 cell line expressing human CYP2E1. Two methods were used to study the CYP2E1 turnover; after addition of cycloheximide, the half-life of the CYP2E1 in the intact cells was about 6 h as detected by PNP catalytic activity assay and immunoblot analysis of apoprotein content. CYP2E1 substrates or ligands such as 4-methylpyrazole, ethanol, glycerol, and dimethyl sulfoxide protected CYP2E1 against this rapid degradation, whereas CCl4 accelerated this process. The second procedure involved pulse-chase experiments after labeling CYP2E1 with [35S]methionine and immunoprecipitation with anti-human CYP2E1 IgG. The half-life of CYP2E1 was about 2.5 h, and the various substrates or ligands modified the turnover process within intact cells as described for the cycloheximide experiments. More than 20 different reagents including antioxidants, physiological metabolites, lysosomal inhibitors, and protease inhibitors were screened for possible effects on CYP2E1 proteolytic degradation. Dibutyryl cAMP had no effect on CYP2E1 activity or turnover. Among those reagents tested so far, the serine protease inhibitor 1-chloro-3-tosylamido-7-amino-2-heptanone hydrochloride exhibited some protection against CYP2E1 degradation. To demonstrate whether the proteasome complex is involved in this process, Czb-Ile-Glu(OtBu)-Ala-leucinal (PSI) as a cell penetrating aldehydic proteasome inhibitor and Czb-Leu-norleucinal (calpeptin inhibitor) as an aldehydic nonproteosomal protease inhibitor were used to examine their effect on both the normal and the CCl4-stimulated CYP2E1 proteolytic degradation pathways. Treatment with PSI at concentrations ranging from 5 to 80 microM resulted in a dose-dependent protection against the loss of both the normal CYP2E1 and the CCl4-modified CYP2E1. The maximum protection by PSI at a concentration of 80 microM after a 12-h chase period was about 60% in cells treated with 2 mM CCl4 or 75% in cells without CCl4 treatment. Calpeptin inhibitor afforded little or no protection against CYP2E1 degradation in the absence or presence of CCl4. PSI did not inhibit CYP2E1 catalytic activity, suggesting that it was not a ligand for CYP2E1. These results indicate that human CYP2E1 has a short half-life span and that substrates can significantly modify its turnover rate in intact HepG2 cells. The proteasome proteolytic pathway may be involved in the degradation process of both the normal and the CCl4-modified human CYP2E1 in this model.
...
PMID:Characterization of cytochrome P4502E1 turnover in transfected HepG2 cells expressing human CYP2E1. 914 49

Proteasomes are the major cytosolic protease complexes responsible for energy-dependent and extra-lysosomal proteolysis. Ubiquitinated proteins are degraded by the 26S proteasome which is composed of a 20S proteasome and two regulatory complexes. Changes in the 20S and 26S proteasome activity levels and protein abundance in spinach seeds during imbibition and germination were examined by using glycerol density gradient centrifugation. The 26S proteasome activity level decreased transiently during imbibition, reached a minimum one day after starting imbibition, and then increased again. During the period of minimal accumulation, the protein being detected with an anti-26S proteasome antibody shifted to a lower sedimentation coefficient fraction. In contrast, the 20S proteasome activity level increased during imbibition, and remained high for two days. The change in the 20S proteasome level corresponded to the change in the 20S proteasome activity level.
...
PMID:Changes in proteasome levels in spinach (Spinacia oleracea) seeds during imbibition and germination. 921 61

African trypanosomes are tsetse-transmitted protozoan parasites that cause sleeping sickness in humans and 'Nagana' in animals. A high relative molecular mass multicatalytic proteinase complex (MCP) was purified and biochemically characterized from the cytosolic fraction of Trypanosoma brucei brucei. The isolation procedure consisted of fractionation of the lysate by high speed centrifugation, chromatography on Q-sepharose molecular sieve filtration on Sephacryl S-300, chromatography on HA-Ultrogel and glycerol density gradient centrifugation (10-40%). The final enzyme preparation yielded a single protein band corresponding to a relative molecular mass of 630 kDa on a non-denaturing polyacrylamide gel. The enzyme hydrolyses a wide range of peptide substrates characteristic of chymotrypsin-like, trypsin-like, peptidylglutamylpeptide-hydrolysing activities determined by fluorogenic peptides, Z-Gly-Gly-Leu-NHMec, Z-Arg-Arg-NHMec and Z-Leu-Leu-Glu-beta NA, respectively. The enzyme was found to have a wide variation in pH optimal activity profile, with optimum activity against Z-Gly-Gly-Leu-NHMec at 7.8, Z-Arg-Arg-NHMec at pH 10.5 and Z-Leu-Leu-Glu-beta NA at pH 8.0, showing that the different activities are distinct. The enzyme hydrolysed oxidized proteins. In addition, the chymotryptic and trypsin-like activities were susceptible to inhibition by peptide aldehyde inhibitors with variable inhibition effects. The study demonstrates the presence of a non-lysosomal proteasome pathway of intracellular protein degradation in the bloodstream form of T. b. brucei. Further, the ability of the enzyme to hydrolyse most oxidized proteins, and the high immunogenicity exhibited suggests a possible involvement of the enzyme in pathogenesis of the disease.
...
PMID:Characterization of a multicatalytic proteinase complex (20S proteasome) from Trypanosoma brucei brucei. 922 59

We purified by fractionation on 10-40% glycerol gradients, 26S proteasomes from normal human spermatozoa. These proteasomes, which participate in the ATP-dependent degradation of ubiquitinated proteins, share a similar sedimentation coefficient to those purified from other human tissues. Fluorogenic peptide assays reveal they have chymotrypsin, trypsin and peptidyl-glutamyl-like peptide hydrolysing activities; the chymotrypsin activity is ablated by the specific 26S proteasome inhibitor MG132. Confirmation that these large proteases are 26S proteasomes is provided by detection of the 20S proteasome subunits HC2, XAPC7, RN3 and Z and regulatory ATPases MSS1, TBP1, SUG1 and SUG2 by Western analyses with monoclonal antisera. These antigens are found only in the gradient fractions enriched in proteolytic activities. We have also shown that, although mature spermatozoa from mice have considerably reduced amounts of a ubiquitin-conjugating enzyme (E2) and ubiquitin-protein conjugates in comparison with less mature germ cells, they retain relatively high values of 26S proteasome activity. This suggests that proteasomes may have further roles to play in normal sperm physiology.
...
PMID:Purification and characterization of 26S proteasomes from human and mouse spermatozoa. 946 50

Accumulation of altered proteins in old animals has been ascribed to slower turnover of proteins. Since proteasomes can be regarded as the major proteolytic enzymes responsible for the degradation of the majority of cellular proteins, we examined age-related changes of 20S and 26S proteasomes in the liver of young (8-10-month-old), middle-aged (15-18-month-old) and old (25-28-month-old) Fischer 344 male rats. The two forms of proteasomes were separated by glycerol gradient centrifugation. Fluorogenic peptides were used as substrates to evaluate three types of peptidase activities. The ratio of peptidase activities in the 20S proteasome vs. those in the 26S form did not appear to change with age. Unstimulated chymotrypsin-like activity found only in the 26S form decreased by 30% in the old rats as compared with that in the young ones, while no change in the activity was observed during aging when stimulated by sodium dodecyl sulfate. The trypsin-like activity declined significantly by 17% to an apparently similar extent in both 20S and 26S forms. The peptidylglutamyl peptide hydrolyzing activity exhibited gradual decrease with age, resulting in 60% lower value in the old rats as compared with the young animals. These changes are considered to account for the age-related extension of half-life of proteins. Since the amount of total proteasomes measured by immunoblot did not appear to change with age, posttranslational modifications or subunit replacement is possibly responsible for the decrease in the activities.
...
PMID:Age-related changes in the 20S and 26S proteasome activities in the liver of male F344 rats. 966 92

hHR23B is one of two human homologs of the Saccharomyces cerevisiae nucleotide excision repair (NER) gene product RAD23 and a component of a protein complex that specifically complements the NER defect of xeroderma pigmentosum group C (XP-C) cell extracts in vitro. Although a small proportion of hHR23B is tightly complexed with the XP-C responsible gene product, XPC protein, a vast majority exists as an XPC-free form, indicating that hHR23B has additional functions other than NER in vivo. Here we demonstrate that the human NER factor hHR23B as well as another human homolog of RAD23, hHR23A, interact specifically with S5a, a subunit of the human 26 S proteasome using the yeast two-hybrid system. Furthermore, hHR23 proteins were detected with S5a at the position where 26 S proteasome sediments in glycerol gradient centrifugation of HeLa S100 extracts. Intriguingly, hHR23B showed the inhibitory effect on the degradation of (125)I-lysozyme in the rabbit reticulocyte lysate. hHR23 proteins thus appear to associate with 26 S proteasome in vivo. From co-precipitation experiments using several series of deletion mutants, we defined the domains in hHR23B and S5a that mediate this interaction. From these results, we propose that part of hHR23 proteins are involved in the proteolytic pathway in cells.
...
PMID:Interaction of hHR23 with S5a. The ubiquitin-like domain of hHR23 mediates interaction with S5a subunit of 26 S proteasome. 1048 53

We have isolated the RPN9 gene by two-hybrid screening with, as bait, RPN10 (formerly SUN1), which encodes a multiubiquitin chain receptor residing in the regulatory particle of the 26S proteasome. Rpn9 is a nonessential subunit of the regulatory particle of the 26S proteasome, but the deletion of this gene results in temperature-sensitive growth. At the restrictive temperature, the Deltarpn9 strain accumulated multiubiquitinated proteins, indicating that the RPN9 function is needed for the 26S proteasome activity at a higher temperature. We analyzed the proteasome fractions separated by glycerol density gradient centrifugation by native polyacrylamide gel electrophoresis and found that a smaller amount of the 26S proteasome was produced in the Deltarpn9 cells and that the 26S proteasome was shifted to lighter fractions than expected. The incomplete proteasome complexes were found to accumulate in the Deltarpn9 cells. Furthermore, Rpn10 was not detected in the fractions containing proteasomes of the Deltarpn9 cells. These results indicate that Rpn9 is needed for incorporating Rpn10 into the 26S proteasome and that Rpn9 participates in the assembly and/or stability of the 26S proteasome.
...
PMID:Rpn9 is required for efficient assembly of the yeast 26S proteasome. 1049 May 97


<< Previous 1 2 3 4 5 6 7 8 Next >>

---