Mimicking Dimethylallyltryptophan Synthase: Experimental Evidence for a Biosynthetic Cope Rearrangement Process

2012 ◽  
Vol 124 (46) ◽  
pp. 11682-11684 ◽  
Author(s):  
Darius D. Schwarzer ◽  
Philipp J. Gritsch ◽  
Tanja Gaich
Keyword(s):  
Experimental Evidence ◽  
Cope Rearrangement ◽  
Dimethylallyltryptophan Synthase ◽  
Rearrangement Process

The Cope Rearrangement of 1,5-Dimethylsemibullvalene-2(4)-d1 : Experimental Evidence for Heavy-Atom Tunneling

2017 ◽  
Vol 129 (36) ◽  
pp. 10886-10889 ◽  
Author(s):  
Tim Schleif ◽  
Joel Mieres-Perez ◽  
Stefan Henkel ◽  
Melanie Ertelt ◽  
Weston Thatcher Borden ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Heavy Atom ◽  
Cope Rearrangement

Rearrangements in the mechanisms of the indole alkaloid prenyltransferases

2013 ◽  
Vol 85 (10) ◽  
pp. 1935-1948 ◽  
Author(s):  
Niusha Mahmoodi ◽  
Qi Qian ◽  
Louis Y. P. Luk ◽  
Martin E. Tanner
Keyword(s):  
Indole Alkaloid ◽  
Ion Pair ◽  
Pair Formation ◽  
Tryptophan Residue ◽  
Cope Rearrangement ◽  
Indole Ring ◽  
Structural Homology ◽  
Dimethylallyl Diphosphate ◽  
Free Tryptophan ◽  
Dimethylallyltryptophan Synthase

The indole prenyltransferases are a family of metal-independent enzymes that catalyze the transfer of a prenyl group from dimethylallyl diphosphate (DMAPP) onto the indole ring of a tryptophan residue. These enzymes are remarkable in their ability to direct the prenyl group in either a “normal” or “reverse” fashion to positions with markedly different nucleophilicity. The enzyme 4-dimethylallyltryptophan synthase (4-DMATS) prenylates the non-nucleophilic C-4 position of the indole ring in free tryptophan. Evidence is presented in support of a mechanism that involves initial ion pair formation followed by a reverse prenylation at the nucleophilic C-3 position. A Cope rearrangement then generates the C-4 normal prenylated intermediate and deprotonation rearomatizes the indole ring. The enzyme tryprostatin B synthase (FtmPT1) catalyzes the normal C-2 prenylation of the indole ring in brevianamide F (cyclo-L-Trp-L-Pro). It shares high structural homology with 4-DMATS, and evidence is presented in favor of an initial C-3 prenylation (either normal or reverse) followed by carbocation rearrangements to give product. The concept of a common intermediate that partitions to different products via rearrangements can help to explain how these evolutionarily related enzymes can prenylate different positions on the indole ring.

The Cope Rearrangement of 1,5-Dimethylsemibullvalene-2(4)-d1 : Experimental Evidence for Heavy-Atom Tunneling

2017 ◽  
Vol 56 (36) ◽  
pp. 10746-10749 ◽  
Author(s):  
Tim Schleif ◽  
Joel Mieres-Perez ◽  
Stefan Henkel ◽  
Melanie Ertelt ◽  
Weston Thatcher Borden ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Heavy Atom ◽  
Cope Rearrangement

A Cope Rearrangement in the Reaction Catalyzed by Dimethylallyltryptophan Synthase?

2011 ◽  
Vol 133 (32) ◽  
pp. 12342-12345 ◽  
Author(s):  
Louis Y. P. Luk ◽  
Qi Qian ◽  
Martin E. Tanner
Keyword(s):  
Cope Rearrangement ◽  
Dimethylallyltryptophan Synthase

How do memory modules differentially contribute to familiarity and recollection?

2019 ◽  
Vol 42 ◽  
Author(s):  
Olya Hakobyan ◽  
Sen Cheng
Keyword(s):  
Recognition Memory ◽  
Experimental Evidence ◽  
Subjective Experience ◽  
Target Article ◽  
Memory Modules ◽  
Familiarity And Recollection ◽  
Memory Contents

Abstract We fully support dissociating the subjective experience from the memory contents in recognition memory, as Bastin et al. posit in the target article. However, having two generic memory modules with qualitatively different functions is not mandatory and is in fact inconsistent with experimental evidence. We propose that quantitative differences in the properties of the memory modules can account for the apparent dissociation of recollection and familiarity along anatomical lines.

Redox Reactions in Lipid Membranes as a Model for Primordial Energy-Conserving Systems

1997 ◽  
Vol 161 ◽  
pp. 437-442
Author(s):  
Salvatore Di Bernardo ◽  
Romana Fato ◽  
Giorgio Lenaz
Keyword(s):  
Experimental Evidence ◽  
Lipid Membranes ◽  
Energy Supply ◽  
Redox Reactions ◽  
Living Systems ◽  
Asymmetric Distribution ◽  
Conservation Of Energy ◽  
Asymmetrical Distribution ◽  
Energy Conserving ◽  
Living Organisms

AbstractOne of the peculiar aspects of living systems is the production and conservation of energy. This aspect is provided by specialized organelles, such as the mitochondria and chloroplasts, in developed living organisms. In primordial systems lacking specialized enzymatic complexes the energy supply was probably bound to the generation and maintenance of an asymmetric distribution of charged molecules in compartmentalized systems. On the basis of experimental evidence, we suggest that lipophilic quinones were involved in the generation of this asymmetrical distribution of charges through vectorial redox reactions across lipid membranes.

A Method for Setting the Clearance Angle

1972 ◽  
Vol 30 ◽  
pp. 388-389
Author(s):  
Michael T. Bucek ◽  
Howard J. Arnott
Keyword(s):  
Experimental Evidence ◽  
Light Source ◽  
Black Spot ◽  
Critical Factor ◽  
Clearance Angle ◽  
Crude Approximation ◽  
Ultrathin Sections

It is believed by the authors, with supporting experimental evidence, that as little as 0.5°, or less, knife clearance angle may be a critical factor in obtaining optimum quality ultrathin sections. The degree increments located on the knife holder provides the investigator with only a crude approximation of the angle at which the holder is set. With the increments displayed on the holder one cannot set the clearance angle precisely and reproducibly. The ability to routinely set this angle precisely and without difficulty would obviously be of great assistance to the operator. A device has been contrived to aid the investigator in precisely setting the clearance angle. This device is relatively simple and is easily constructed. It consists of a light source and an optically flat, front surfaced mirror with a minute black spot in the center. The mirror is affixed to the knife by placing it permanently on top of the knife holder.

Introductory Remarks

1980 ◽  
Vol 38 ◽  
pp. 598-599
Author(s):  
H. Mohri
Keyword(s):  
Muscle Contraction ◽  
Experimental Evidence ◽  
Sea Urchin ◽  
Constant Length ◽  
Thin Filaments ◽  
Bridge Formation ◽  
Thick Filaments ◽  
Sliding Mechanism ◽  
Radial Spokes ◽  
Cilia And Flagella

In 1959, Afzelius observed the presence of two rows of arms projecting from each outer doublet microtubule of the so-called 9 + 2 pattern of cilia and flagella, and suggested a possibility that the outer doublet microtubules slide with respect to each other with the aid of these arms during ciliary and flagellar movement. The identification of the arms as an ATPase, dynein, by Gibbons (1963)strengthened this hypothesis, since the ATPase-bearing heads of myosin molecules projecting from the thick filaments pull the thin filaments by cross-bridge formation during muscle contraction. The first experimental evidence for the sliding mechanism in cilia and flagella was obtained by examining the tip patterns of molluscan gill cilia by Satir (1965) who observed constant length of the microtubules during ciliary bending. Further evidence for the sliding-tubule mechanism was given by Summers and Gibbons (1971), using trypsin-treated axonemal fragments of sea urchin spermatozoa. Upon the addition of ATP, the outer doublets telescoped out from these fragments and the total length reached up to seven or more times that of the original fragment. Thus, the arms on a certain doublet microtubule can walk along the adjacent doublet when the doublet microtubules are disconnected by digestion of the interdoublet links which connect them with each other, or the radial spokes which connect them with the central pair-central sheath complex as illustrated in Fig. 1. On the basis of these pioneer works, the sliding-tubule mechanism has been established as one of the basic mechanisms for ciliary and flagellar movement.

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