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111.
The molecular mechanisms of protein inactivation, i.e. aggregation, thiol-disulphide exchange, alteration of the primary structure, dissociation of cofactor molecules from the active centre, dissociation of the oligomeric proteins into subunits and conformational changes have been analysed. All these mechanisms are closely interrelated during inactivation of proteins. However, in many cases, the conformational changes accompany and trigger other inactivation processes. Reactivation of irreversibly inactivated proteins is·discussed. Reactivation can be successful when inactivation has been caused by aggregation, modification of SH-groups (or S-S bonds) or as a consequence of irreversible conformational changes. 相似文献
112.
The present study contributes to the problem of the dynamic structure of mitochondrial F1-ATPase and the functional interrelation of so-called tight nucleotide binding sites. Nucleotide analogs are used as a tool to differentiate two distinct functional states of the membrane-bound enzyme, proposed to reflect corresponding conformational states; they reveal F1-ATPase as a dual-state enzyme: ATP-synthetase, and ATP-hydrolase. The analogs used are 3-naphthoyl esters of AD(T)P, and 2(3)-O-trinitrophenyl ethers of AD(T)P. Both types of analogs act inversely to each other with respect to their relative effects on oxidative phosphorylation and on ATPase in submitochondrial vesicles. The respective ratios ofK
i versus both processes are 250/1 compared to 1/170. It is also shown that in the presence of the inhibitory 3-esters oxidative phosphorylation deviates from linear kinetics and that these inhibitors induce a lag time of oxidative phosphorylation depending on the initial pattern of nucleotides available to energized submitochondrial vesicles. The duration of the lag time coincides with the time course of displacement of the analog from a tight binding site. The conclusions of the study are: (a) the catalytic sites of F1-ATP-synthetase are not operating independently from each other; they rather interact in a cooperative manner; (b) F1-ATPase as a dual-state enzyme exhibits highly selective responses to tight binding of nucleotides or analogs in its energized (membrane-bound) state versus its nonenergized state, respectively.Abbreviations used: N-AD(T)P, 3-O-naphthoyl(1)-AD(T)P; DMAN-AD(T)P, 3-O-(5-dimethylaminonaphthoyl(1))-AD(T)P, also termed F-AD(T)P in previous papers because of its fluorescence; TNP-AD(T)P, 2(3)-O-(2,4,6-trinitrophenyl)-AD(T)P; FCCP,p-trifluoromethoxycarbonylcyanide phenylhydrazone. 相似文献
113.
114.
Ross H. Hall 《In vitro cellular & developmental biology. Plant》1976,12(3):216-224
Summary Cells possess extraordinary powers to organize their molecular processes not only to maintain a cell in a given steady state
but also to recognize that state during differentiation. Regulation of these organizational forces appears to be under the
control of chemical factors, and a hormonal concept of regulation has evolved. Hormones have been considered to act by reacting
with a specific target site. This may be part of their mode of action, but I would like to suggest that a hormone enters and
becomes part of a total molecular resonance system. In so doing, the entire molecular system of the cell is modified.
Of the known plant hormones, the cytokinins, because of their role in experimentally induced cell division and differentiation,
serve as a probe of hormonal involvement in differentiation. Cultured somatic cells of tobacco plants can be induced to undergo
differentiation by addition of cytokinin and auxin to the medium. Studies of the cytokinin hormones show a series of diverse
molecular involvements. The archetype cytokinin, N6-(Δ2-isopentenyl) adenosine (i6Ado), occurs in some molecular species of tRNA where it plays a vital role in the codon-anticodon interaction of tRNA and
m-RNA. i6Ado under-goes extensive metabolism in the tobacco tissue. It is either degraded to adenosine or converted to derivatives
that possess biological activity. It is perhaps, therefore, more correct to consider the hormone function as being derived
from this total metabolic web.
The normal somatic cells of tobacco cultures spontaneously change occasionally into an autonomous form that requires no external
growth factors. This line of cells synthesizes i6Ado. The metabolic web of the hormone-dependent strain can be perturbed by added auxin but such is not the case in the autonomous
strain. These data provide some insight into the altered state of cytokinin activity in which a cell line changes into an
autonomous form. Curiously, in become independent of the requirement for exogenous cytokinin, the autonomous tissue becomes
sensitive to added cytokinin. i6Ado also inhibits the growth of lines of mammalian cancer cells grown in culture.
Presented in the formal symposium on Information Transfer in Eukaryotic Cells, at the 26th Annual Meeting of the Tissue Culture
Association, Montreal, Quebec, June 2–5, 1975. 相似文献
115.
Sven Erik Rognes 《Phytochemistry》1975,14(9):1975-1982
Asparagine synthetase (glutamine-hydrolyzing [l-aspartate: l-glutamine amido-ligase (AMP-forming), E.C. 6.3.5.4] was purified over 500-fold from cotyledon extracts of 1-week-old yellow lupin seedlings. The enzyme was labile and required protection by high levels of thiols; glycerol and the substrates also stabilized it. The reaction products were shown to be asparagine, AMP, PPi and glutamate. The limiting Km values were for aspartate 1·3 mM, for MgATP 0·14 mM and for glutamine 0·16 mM. Positive homotropic cooperativity was observed for MgATP only, and gel filtration studies indicated that the substrate-free enzyme (MW 160 000) associated to a dimer (MW 320 000 in the presence of MgCl2 and ATP. The purified enzyme, which had some glutaminase activity, catalyzed an aspartate- and glutamine-independent ATP-PPi exchange reaction at a rate 5–7-fold higher than the rate of asparagine synthesis. Initial velocity studies and exchange data indicated an overall ping-pong mechanism. Compared to similar enzymes isolated from mammalian tumor cells, the lupin enzyme appears to be unique with respect to MW, reaction mechanism and regulatory properties. The allosteric properties observed suggest an important role for this enzyme in the regulation of asparagine biosynthesis. 相似文献
116.
The increasing resistance of pathogens to common antibiotics, as well as the need to control urease activity to improve the yield of soil nitrogen fertilization in agricultural applications, has stimulated the development of novel classes of molecules that target urease as an enzyme. In this context, the newly developed compounds on the basis of 1-heptanoyl-3-arylthiourea family were evaluated for Jack bean urease enzyme inhibition activity to validate their role as potent inhibitors of this enzyme. 1-Heptanoyl-3-arylthioureas were obtained in excellent yield and characterized through spectral and elemental analysis. All the compounds displayed remarkable potency against urease inhibition as compared to thiourea standard. It was found that novel compounds fulfill the criteria of drug-likeness by obeying Lipinski’s rule of five. Particularly compound 4a and 4c can serve as lead molecules in 4D (drug designing discovery and development). Kinetic mechanism and molecular docking studies also carried out to delineate the mode of inhibition and binding affinity of the molecules. 相似文献
117.
118.
119.
The direct HPLC separation of three chiral carbinols of general formula Mesityl-CH(OH)-Aryl has been achieved using Pirkle (R)-DNBPG ionic or covalent columns and, for Aryl = o-tolyl, on a Chiralpak OP(+) phase. It is apparent that steric hindrance and hydrogen bonding play important roles in chiral recognition. Two compounds structurally very similar but lacking the hydroxyl group were not resolved in their enantiomeric pairs. © 1992 Wiley-Liss, Inc. 相似文献
120.
Based on the high-resolution X-ray crystallographic structure of phospholipase C from Bacillus cereus, the orientation of the phosphatidylcholine substrate in the active site of the enzyme is proposed. The proposal is based on extensive calculations using the GRID program and molecular mechanics geometry relaxations. The substrate model has been constructed by successively placing phosphate, choline and diacylglycerol moieties in the positions indicated from GRID calculations. On the basis of the resulting orientation of a complete phosphatidylcholine molecule, we propose a mechanism for the hydrolysis of the substrate. 相似文献