Computational Modeling of the Optical Rotation of Amino Acids:  A New Look at an Old Rule for pH Dependence of Optical Rotation

2008 ◽  
Vol 130 (13) ◽  
pp. 4404-4414 ◽  
Author(s):  
Matthew D. Kundrat ◽  
Jochen Autschbach
Keyword(s):  
Amino Acids ◽  
Computational Modeling ◽  
Optical Rotation ◽  
Ph Dependence ◽  
New Look

Homochirality as the Signature of Extra-Terrestrial Life

1997 ◽  
Vol 161 ◽  
pp. 505-510
Author(s):  
Alexandra J. MacDermott ◽  
Laurence D. Barron ◽  
Andrè Brack ◽  
Thomas Buhse ◽  
John R. Cronin ◽  
...  
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Optical Rotation ◽  
Physical Origin ◽  
Natural Choice ◽  
Rosetta Mission ◽  
Terrestrial Life ◽  
Subsurface Layers ◽  
Solar System Bodies ◽  
Origin Of Homochirality

AbstractThe most characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. We therefore suggest that a search for extra-terrestrial life can be approached as a Search for Extra- Terrestrial Homochirality (SETH). The natural choice for a SETH instrument is optical rotation, and we describe a novel miniaturized space polarimeter, called the SETH Cigar, which could be used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. We believe that homochirality may be found in the subsurface layers on Mars as a relic of extinct life, and on other solar system bodies as a sign of advanced pre-biotic chemistry. We discuss the chiral GC-MS planned for the Roland lander of the Rosetta mission to a comet and conclude with theories of the physical origin of homochirality.

The Bβ-sheet in the PAI-1 Molecule Plays an Important Role for Its Stability

2000 ◽  
Vol 83 (06) ◽  
pp. 896-901 ◽  
Author(s):  
Guang-Chao Sui ◽  
Björn Wiman
Keyword(s):  
Amino Acids ◽  
Half Life ◽  
Ph Dependence ◽  
The Other ◽  
Wild Type ◽  
E Coli ◽  
Reactive Center ◽  
The Stability ◽  
Β Sheet ◽  
Pai 1

SummaryWe have investigated the B β-sheet in PAI-1 regarding its role for the stability of the molecule. The residues from His219 to Tyr241 (except for Gly230 and Pro240), covering the s2B and s3B strands, and in addition His185 and His190 were substituted by amino acids with opposite properties. The 23 generated single-site changed mutants and also wild type PAI-1 (wtPAI-1) were expressed in E. coli. Subsequently they were purified by heparin-Sepharose and anhydrotrypsin agarose affinity chromatographies. The stability of the purified PAI-1 variants was analyzed at 37° C and at different pHs (5.5, 6.5 or 7.5). At pH 7.5 and 37° C, single substitutions of the residues in the central portions of both strands 2 and 3 in the B β-sheet (Ile223 to Leu226 on s2B and Met235 to Ile237 on s3B), caused a significant decrease in stability, yielding half-lives of about 10–25% as compared to wtPAI-1. On the other hand, mutations at both sides of the central portion of the B β-sheet (Tyr221, Asp222, Tyr228 and Thr232) frequently resulted in an increased PAI-1 stability (up to 7-fold). While wtPAI-1 exhibited prolonged half-lives at pH 6.5 and 5.5, the PAI-1 variant Y228S was more stable at neutral pH (half-life of 9.6 h at pH 7.5) as compared to its half-life at pH 5.5 (1.1 h). One of the 4 modified histidine residues (His229) resulted in a variant with a clearly affected stability as a function of pH, suggesting that it may, at least in part, be of importance for the pH dependence of the PAI-1 stability. Thus, our data demonstrate that the B β-sheet is of great importance for the stability of the molecule. Modifications in this part causes decreased or increased stability in a certain pattern, suggesting effects on the insertion rate of the reactive center loop into the A β-sheet of the molecule.

Lemon Juice Composition. I. Characterization of California-Arizona Lemon Juice by Its Total Amino Acid and l-Malic Acid Content

1963 ◽  
Vol 46 (3) ◽  
pp. 353-358 ◽  
Author(s):  
Carl E Vandercook ◽  
Laurence A Rolle ◽  
Robert M Ikeda
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Malic Acid ◽  
Acid Content ◽  
Optical Rotation ◽  
Lemon Juice ◽  
Total Amino Acid ◽  
The Individual ◽  
Composition I ◽  
Total Amino Acids

Abstract The total amino acid and i-malic acid content of 61 samples of commercial California-Arizona lemon juice and lemon juice concentrates were studied. In characterizing these juices, relationships were observed between the natural citric acid content and the amounts of their total amino acids and l-malic acid. Total amino acids were determined by formol titration, while the l-malic acid was determined by measuring the optical rotation of a uranylmalate complex. Paper chromatograms of the individual amino acids are used to supplement these methods of analysis for characterizing lemon juice.

Characterization of active-site residues in diadenosine tetraphosphate hydrolase from Lupinus angustifolius

2001 ◽  
Vol 357 (2) ◽  
pp. 399-405 ◽  
Author(s):  
Danuta MAKSEL ◽  
Paul R. GOOLEY ◽  
James D. SWARBRICK ◽  
Andrzej GURANOWSKI ◽  
Christine GANGE ◽  
...  
Keyword(s):  
Amino Acids ◽  
Metal Ion ◽  
Solution Structure ◽  
Ph Dependence ◽  
Three Dimensional ◽  
Lupinus Angustifolius ◽  
Site Directed Mutagenesis ◽  
Nudix Hydrolase ◽  
Active Site Residues ◽  
Dimensional Solution

Site-directed mutagenesis has been used to characterize the functions of key amino acid residues in the catalytic site of the ‘nudix’ hydrolase, (asymmetrical) diadenosine 5′,5‴-P1,P4-tetraphosphate (Ap4A) hydrolase (EC 3.6.1.17) from Lupinus angustifolius, the three-dimensional solution structure of which has recently been solved. Residues within the nudix motif, Gly-(Xaa)5-Glu-(Xaa)7-Arg-Glu-Uaa-Xaa-(Glu)2-Xaa-Gly (where Xaa represents unspecified amino acids and Uaa represents the bulky aliphatic amino acids Ile, Leu or Val) conserved in ‘nudix enzymes’, and residues important for catalysis from elsewhere in the molecule, were mutated and the expressed proteins characterized. The results reveal a high degree of functional conservation between lupin asymmetric Ap4A hydrolase and the 8-oxo-dGTP hydrolase from Escherichia coli. Charged residues in positions equivalent to those that ligate an enzyme-bound metal ion in the E. coli 8-oxo-dGTP hydrolase [Harris, Wu, Massiah and Mildvan (2000) Biochemistry 39, 1655–1674] were shown to contribute to catalysis to similar extents in the lupin enzyme. Mutations E55Q, E59Q and E125Q all reduced kcat markedly, whereas mutations R54Q, E58Q and E122Q had smaller effects. None of the mutations produced a substantial change in the Km for Ap4A, but several extensively modified the pH-dependence and fluoride-sensitivities of the hydrolase. It was concluded that the precisely positioned glutamate residues Glu-55, Glu-59 and Glu-125 are conserved as functionally significant components of the hydrolytic mechanism in both of these members of the nudix family of hydrolases.

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