The amino acid sequence of Neurospora NADP-specific glutamate dehydrogenase. The tryptic peptides.
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The NADP-specific glutamate dehydrogenase of Neurospora crassa was digested with trypsin, and peptides accounting for 441 out of the 452 residues of the polypeptide chain were isolated and substantially sequenced. Additional experimental detail has been deposited as Supplementary Publication SUP 50052 (11 pages) with the British Library (Lending Division), Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K., from whom copies may be obtained under the terms given in Biochem J. (1975) 145, 5. (+info)
The effects of digestive enzymes on characteristics of placental insulin receptor. Comparison of particulate and soluble receptor preparations.
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The role of the surrounding membrane structure on the binding characteristics of the insulin receptor was studied by using several digestive enzymes. The effects observed with particulate membrane preparations are compared with those from soluble receptor preparations. beta-Galactosidase and neuraminidase had no effect on insulin binding to either particulate or soluble receptors from human placentae. Exposure to 2 units of phospholipase C/ml increased insulin binding to particulate membranes, but was without effect on the soluble receptor preparation. The increase in binding to particulate membranes was shown to be due to an increase in apparent receptor number. After 5 min exposure to 500 microgram of trypsin/ml there was an increase in insulin binding to the particulate membrane fraction, owing to an increase in receptor affinity. After 15 min exposure to this amount of trypsin, binding decreased, owing to a progressive decrease in receptor availability. In contrast, this concentration of trypsin had no effect on the solubilized receptor preparation. Because of the differential effects of phospholipase C and trypsin on the particulate compared with the solubilized receptor preparations, it is concluded that the effects of these enzymes were due to an effect on the surrounding membrane structure. Changes in receptor configuration due to alterations within the adjoining membrane provide a potential mechanism for mediating short-term alterations in receptor function. (+info)
Stable remodeling of tailless nucleosomes by the human SWI-SNF complex.
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The histone N-terminal tails have been shown previously to be important for chromatin assembly, remodeling, and stability. We have tested the ability of human SWI-SNF (hSWI-SNF) to remodel nucleosomes whose tails have been cleaved through a limited trypsin digestion. We show that hSWI-SNF is able to remodel tailless mononucleosomes and nucleosomal arrays, although hSWI-SNF remodeling of tailless nucleosomes is less effective than remodeling of nucleosomes with tails. Analogous to previous observations with tailed nucleosomal templates, we show both (i) that hSWI-SNF-remodeled trypsinized mononucleosomes and arrays are stable for 30 min in the remodeled conformation after removal of ATP and (ii) that the remodeled tailless mononucleosome can be isolated on a nondenaturing acrylamide gel as a novel species. Thus, nucleosome remodeling by hSWI-SNF can occur via interactions with a tailless nucleosome core. (+info)
The C-terminal region of hPrp8 interacts with the conserved GU dinucleotide at the 5' splice site.
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A U5 snRNP protein, hPrp8, forms a UV-induced crosslink with the 5' splice site (5'SS) RNA within splicing complex B assembled in trans- as well as in cis-splicing reactions. Both yeast and human Prp8 interact with the 5'SS, branch site, polypyrimidine tract, and 3'SS during splicing. To begin to define functional domains in Prp8 we have mapped the site of the 5'SS crosslink within the hPrp8 protein. Immunoprecipitation analysis limited the site of crosslink to the C-terminal 5060-kDa segment of hPrp8. In addition, size comparison of the crosslink-containing peptides generated with different proteolytic reagents with the pattern of fragments predicted from the hPrp8 sequence allowed for mapping of the crosslink to a stretch of five amino acids in the C-terminal portion of hPrp8 (positions 1894-1898). The site of the 5'SS:hPrp8 crosslink falls within a segment spanning the previously defined polypyrimidine tract recognition domain in yPrp8, suggesting that an overlapping region of Prp8 may be involved both in the 5'SS and polypyrimidine tract recognition events. In the context of other known interactions of Prp8, these results suggest that this protein may participate in formation of the catalytic center of the spliceosome. (+info)
Re-entering the translocon from the lumenal side of the endoplasmic reticulum. Studies on mutated carboxypeptidase yscY species.
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Misfolded or unassembled secretory proteins are retained in the endoplasmic reticulum (ER) and subsequently degraded by the cytosolic ubiquitin-proteasome system. This requires their retrograde transport from the ER lumen into the cytosol, which is mediated by the Sec61 translocon. It had remained a mystery whether ER-localised soluble proteins are at all capable of re-entering the Sec61 channel de novo or whether a permanent contact of the imported protein with the translocon is a prerequisite for retrograde transport. In this study we analysed two new variants of the mutated yeast carboxypeptidase yscY, CPY*: a carboxy-terminal fusion protein of CPY* and pig liver esterase and a CPY* species carrying an additional glycosylation site at its carboxy-terminus. With these constructs it can be demonstrated that the newly synthesised CPY* chain is not retained in the translocation channel but reaches its ER lumenal side completely. Our data indicate that the Sec61 channel provides the essential pore for protein transport through the ER membrane in either direction; persistent contact with the translocon after import seems not to be required for retrograde transport. (+info)
Reaction specificity of native and nicked 3,4-dihydroxyphenylalanine decarboxylase.
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3,4-Dihydroxyphenylalanine (Dopa) decarboxylase is a stereospecific pyridoxal 5'-phosphate (PLP)-dependent alpha-decarboxylase that converts L-aromatic amino acids into their corresponding amines. We now report that reaction of the enzyme with D-5-hydroxytryptophan or D-Dopa results in a time-dependent inactivation and conversion of the PLP coenzyme to pyridoxamine 5'-phosphate and PLP-D-amino acid Pictet-Spengler adducts, which have been identified by high performance liquid chromatography. We also show that the reaction specificity of Dopa decarboxylase toward aromatic amines depends on the experimental conditions. Whereas oxidative deamination occurs under aerobic conditions (Bertoldi, M., Moore, P. S., Maras, B., Dominici, P., and Borri Voltattorni, C. (1996) J. Biol. Chem. 271, 23954-23959; Bertoldi, M., Dominici, P., Moore, P. S., Maras, B., and Borri Voltattorni, C. (1998) Biochemistry 37, 6552-6561), half-transamination and Pictet-Spengler reactions take place under anaerobic conditions. Moreover, we examined the reaction specificity of nicked Dopa decarboxylase, obtained by selective tryptic cleavage of the native enzyme between Lys334 and His335. Although this enzymatic species does not exhibit either decarboxylase or oxidative deamination activities, it retains a large percentage of the native transaminase activity toward D-aromatic amino acids and displays a slow transaminase activity toward aromatic amines. These transamination reactions occur concomitantly with the formation of cyclic coenzyme-substrate adducts. Together with additional data, we thus suggest that native Dopa decarboxylase can exist as an equilibrium among "open," "half-open," and "closed" forms. (+info)
Enrichment of enzyme activity on deformylation of 1-NFK-lysozyme.
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The formamide linkage of an inactive lysozyme derivative (1-NFK-lysozyme), formed by selective ozonization of tryptophan 62 in hen egg-white lysozyme [EC 3.2.1.17] was hydrolyzed with dilute acid faster in the frozen state at about --10 degrees than at 20 degrees. On hydrolysis of 1-NFK-lysozyme the low lytic activity increased to approximately 80% of that of native lysozyme. It is suggested that the binding ability associated with kynurenine 62 in the lysozyme derivative formed by this hydrolysis may be responsible for increase in enzymatic activity. (+info)
Further studies on the mechanism of adrenaline-induced lipolysis in lipid micelles.
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Lipase [EC 3.1.1.3] depleted lipid micelles, in which lipolysis was not elicited by adrenaline, were prepared from lipid micelles. When these lipase-depleted lipid micelles incubated with adipose tissue extract containing lipase activity, adrenaline-induced lipolysis was restored to almost the same level as that of native lipid micelles. Adrenaline-induced lipolysis was not restored when the lipase-depleted lipid micelles were homogenized or sonicated. Various tissue extracts from kidney, lung, liver, and pancreas, and post-heparin plasma, which contained lipase activity, restored adrenaline-induced lipolysis in lipase-depleted lipid micelles. (+info)