排序方式: 共有53条查询结果,搜索用时 31 毫秒
41.
Kunihiko SAITO 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2014,90(9):333-346
Since the phospholipase B (PLB) was reported as a deacylase of both lecithin and lysolecithin yielding fatty acids and glycerophosphocholine (GPC), there was a question as to whether it is a single enzyme or a mixture of a phospholipase A2 (PLA2) and a lysophospholipase (LPL). We purified the PLB in Penicillium notatum and showed that it catalyzed deacylation of sn-1 and sn-2 fatty acids of 1,2-diacylphospholipids and also sn-1 or sn-2 fatty acids of 1- or 2-monoacylphospholipids (lysophospholipids). Further, it also has a monoacyllipase activity. The purified PLB is a glycoprotein with m.w. of 91,300. The sugar moiety is M9 only and the protein moiety consists of 603 amino acids. PLB, different from PLA2, shows other enzymatic activities, such as transacylase, lipase and acylesterase. PLB activity is influenced by various substances, e.g. detergents, deoxycholate, diethylether, Fe3+, and endogenous protease. Therefore, PLB might have broader roles than PLA2
in vivo. The database shows an extensive sequence similarity between P. notatum PLB and fungal PLB, cPLA2 and patatin, suggesting a homologous relationship. The catalytic triad of cPLA2, Ser, Asp and Arg, is also present in P. notatum PLB. Other related PLBs, PLB/Lipases are discussed. 相似文献
42.
43.
Dr. Carla S. Silva Teixeira Dr. Sérgio F. Sousa Dr. Nuno M. F. S. A. Cerqueira 《Chemphyschem》2021,22(8):796-804
Nitrilase 2 (Nit2) is a representative member of the nitrilase superfamily that catalyzes the hydrolysis of α-ketosuccinamate into oxaloacetate. It has been associated with the metabolism of rapidly dividing cells like cancer cells. The catalytic mechanism of Nit2 employs a catalytic triad formed by Cys191, Glu81 and Lys150. The Cys191 and Glu81 play an active role during the catalytic process while the Lys150 is shown to play only a secondary role. The results demonstrate that the catalytic mechanism of Nit2 involves four steps. The nucleophilic attack of Cys191 to the α-ketosuccinamate, the formation of two tetrahedral enzyme adducts and the hydrolysis of a thioacyl-enzyme intermediate, from which results the formation of oxaloacetate and enzymatic turnover. The rate limiting step of the catalytic process is the formation of the first tetrahedral intermediate with a calculated activation free energy of 18.4 kcal/mol, which agrees very well with the experimental kcat (17.67 kcal/mol). 相似文献
44.
Yunseok Heo Inhwan Lee Sunjin Moon Ji-Hye Yun Eun Yu Kim Sam-Yong Park Jae-Hyun Park Woo Taek Kim Weontae Lee 《Molecules (Basel, Switzerland)》2022,27(7)
Phospholipase is an enzyme that hydrolyzes various phospholipid substrates at specific ester bonds and plays important roles such as membrane remodeling, as digestive enzymes, and the regulation of cellular mechanism. Phospholipase proteins are divided into following the four major groups according to the ester bonds they cleave off: phospholipase A1 (PLA1), phospholipase A2 (PLA2), phospholipase C (PLC), and phospholipase D (PLD). Among the four phospholipase groups, PLA1 has been less studied than the other phospholipases. Here, we report the first molecular structures of plant PLA1s: AtDSEL and CaPLA1 derived from Arabidopsis thaliana and Capsicum annuum, respectively. AtDSEL and CaPLA1 are novel PLA1s in that they form homodimers since PLAs are generally in the form of a monomer. The dimerization domain at the C-terminal of the AtDSEL and CaPLA1 makes hydrophobic interactions between each monomer, respectively. The C-terminal domain is also present in PLA1s of other plants, but not in PLAs of mammals and fungi. An activity assay of AtDSEL toward various lipid substrates demonstrates that AtDSEL is specialized for the cleavage of sn-1 acyl chains. This report reveals a new domain that exists only in plant PLA1s and suggests that the domain is essential for homodimerization. 相似文献
45.
In order to investigate the origin of catalytic power for serine proteases, the role of the hydrogen bond in the catalytic triad was studied in the proteolysis process of the peptides chymotrypsin inhibitor 2 (CI2), MCTI-A, and a hexapeptide (SUB), respectively. We first calculated the free energy profile of the proton transfer between His and Asp residues of the catalytic triad in the enzyme-substrate state and transition state by employing QM/MM molecular dynamics simulations. The results show that a low-barrier hydrogen bond (LBHB) only forms in the transition state of the acylation of CI2, while it is a normal hydrogen bond in the acylation of MCTI-A or SUB. In addition, the change of the hydrogen bond strength is much larger in CI2 and SUB systems than in MCTI-A system, which decreases the acylation energy barrier significantly for CI2 and SUB. Clearly, a LBHB formed in the transition state region helps accelerate the acylation reaction. But to our surprise, a normal hydrogen bond can also help to decrease the energy barrier. The key to reducing the reaction barrier is the increment of hydrogen bond strength in the transition state state, whether it is a LBHB or not. Our studies cast new light on the role of the hydrogen bond in the catalytic triad, and help to understand the catalytic triad of serine proteases. 相似文献
46.
We present results from ab initio and density functional theory studies of the mechanism for serine hydrolase catalyzed ester hydrolysis. A model system containing both the catalytic triad and the oxyanion hole was studied. The catalytic triad was represented by formate anion, imidazole, and methanol. The oxyanion hole was represented by two water molecules. Methyl formate was used as the substrate. In the acylation step, our computations show that the cooperation of the Asp group and oxyanion hydrogen bonds is capable of lowering the activation barrier by about 15 kcal/mol. The transition state leading to the first tetrahedral intermediate in the acylation step is rate limiting with an activation barrier (ΔE0) of 13.4 kcal/mol. The activation barrier in the deacylation step is smaller. The double-proton-transfer mechanism is energetically unfavorable by about 2 kcal/mol. The bonds between the Asp group and the His group, and the hydrogen bonds in the oxyanion hole, increase in strength going from the Michaelis complex toward the transition state and the tetrahedral intermediate. In the acylation step, the tetrahedral intermediate is a very shallow minimum on the energy surface and is not viable when molecular vibrations are included. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 89–103, 1998 相似文献
47.
48.
Matthias Schork 《Central European Journal of Mathematics》2006,4(3):507-524
It is shown that duality triads of higher rank are closely related to orthogonal matrix polynomials on the real line. Furthermore,
some examples of duality triads of higher rank are discussed. In particular, it is shown that the generalized Stirling numbers
of rank r give rise to a duality triad of rank r. 相似文献
49.
The amidase reaction of trypsin, which is a member of the serine proteinase family, is accelerated by its complexation with block ionomers containing a polycarboxylate block, such as PEG-PAA, PEG-PGA, or PEG-PMA. PEG-PAA and PEG-PGA had similar effects, causing an increase in the k(cat) value and a shift in the pH profile to a lower pH region. On the other hand, PEG-PMA showed not only an increase in the k(cat) value, but also a decrease in the activation energy; however, there was no shift in the pH dependence of the initial reaction rate. Such differences might be induced by the difference in pK(a) values of the polycarboxylate block in block ionomers. 相似文献
50.
A representative acetate-(5-methylimidazole)-methanol system has been employed as a model of catalytic triad in serine protease
to validate the formation processes of low-barrier H-bonds (LBHB) at the B3LYP/6-311++G** level of theory, and variable H-bonding
characters from conventional ones to LBHBs have been represented along with the proceedings of proton transfer. Solvent effect
is an important factor in modulation of the existence of an LBHB, where an LBHB (or a conventional H-bond) in the gas phase
can be changed into a non-LBHB (an LBHB) upon solvation. The origin of the additional stabilization energy arising from the
LBHB may be attributed to the H-bonding energy difference before and after proton transfer because the shared proton can freely
move between the proton donor and proton acceptor. Most importantly, the order of magnitude of the stabilization energy depends
on the studied systems. Furthermore, the nonexistence of LBHBs in the catalytic triad of serine proteases has been verified
in a more sophisticated model treated using the ONIOM method. As a result, only the single proton transfer mechanism in the
catalytic triad has been confirmed and the origin of the powerful catalytic efficiency of serine proteases should be attributed
to other factors rather than the LBHB.
Supported by the National Natural Science Foundation of China (Grant Nos. 20633060 & 20573063), the Natural Science Foundation
of Shandong Province (Grant No. Y2007B23), the Scientific Research Foundation of Qufu Normal University (Grant Nos. Bsqd2007003
and Bsqd2007008), and the State Key Laboratory of Physical Chemistry of Solid Surfaces (Xiamen University) 相似文献