Model studies of competing hydrolysis and epimerization of some tetrapeptides of interest in amino acid racemization studies in geochronology

Abstract

The processes of epimerization of individual peptide units in proteins and the concurrent cleavage of peptide bonds are modelled by heating some tetrapeptide and tetrapeptide derivatives to 148S°C in pH 6.8 phosphate buffer. An excess of D-proline was observed during the heating of L-prolyl-L-leucylglycylglycine. The D/L ratio of proline attains a maximum value of 2.1 after 90 minutes. The excess D-proline is attributed to the formation of a 2.3:1 mixture of diketopiperazines ~y~l~-(D-pr~lyl-L-le~~yl) and cyclo-(L-prolyl-L-leucyl). These two species account for most of the leucine and proline in the final mixture after the tetrapeptide is no longer detectable. Only small amounts of prolylleucine can be detected after 50 hours. It is suggested that the above tetrapeptide undergoes internal aminolysis. Leucine in the tetrapeptide glycyl-L-leucylglycylglycine racemizes three times faster than in L-prolyl-L-leucylglycylglycine. This demonstrates that an amino acid residue in a peptide chain does have an effect upon the rate of epimerization of a neighbouring peptide residue. A discussion of the geochemical implications of the results is included. MICHAEL E. MOIR ET ROBERT J. CRAWFORD. Can. J. Chem. 66,2903Chem. 66, (1988.Afin de dtvelopper un modkle des processus d'tpimtrisation des unitts peptidiques de prottines et du clivage apparent6 des liaisons peptidiques, on a chaufft des tttrapeptides ainsi que leurs dtrivts 148,5"C, dans un tampon de phosphate, a un pH de 6,s. Lorsqu'on a chaufft le L-prolyl-L-leucylglycylglycine, on a observe la formation d'un excks de D-proline. Le rapport de D/L proline atteint une valeur maximale de 2,1 aprks 90 minutes. On attribue la formation d'un excbs de proli line a la formation d'un mtlange 2,3:1 des dicttopiptrazines cyclo-(D-prolyl-L-leucyl) et cyclo-(L-prolyl-L-leucyl). Ces deux espbces peuvent expliquer la formation de la plus grande partie de la leucine ainsi que de la proline prtsentes dans le mtlange final, mCme lorsqu'on ne peut plus dttecter la prtsence du tttrapeptide. On ne peut dttecter la prtsence que de faibles quantitts de prolylleucine aprks 50 heures. On suggkre que le tttrapeptide utilist subit une aminolyse interne. La leucine du tttrapeptide glycyl-L-leucylglycylglycine se ractmise trois fois plus rapidement que dans le L-prolyl-L-leucylglycylglycine. Ce rtsultat dtmontre que le rksidu d'acide amint d'une chaine peptidique influence la vitesse d'tpimtrisation du rtsidu voisin. On prtsente une discussion des implications gtochimiques de nos rksultats.[Traduit par la revue]

Testing the limitations of artificial protein degradation kinetics using known-age massive Porites coral skeletons

“…Kriausakul and Mitterer, 1978 ;Mitterer and Kriausakul, 1984). Racemization of bound amino acids has been hypothesised to occur more rapidly at the N-terminal position (Kriausakul and Mitterer, 1978;Kriausakul and Mitterer, 1980 ;Moir and Crawford, 1988), due to electron withdrawal increasing the ease of abstraction of the hydrogen from the α-carbon (Smith and Reddy, 1989). Racemization of internally bound amino acids is believed to be limited, as demonstrated by the very low D/L values found in high-molecular weight fractions of proteins in a variety of biominerals (e.g.…”

“…Reyes-Grajeda et al, 2004 ;Freeman et al, 2010). Racemization will occur either in denatured stretches (for Asx & Ser; Geiger and Clarke, 1987 ;Takahashi et al, 2010) or at N-terminal (all other amino acids) positions (Kriausakul and Mitterer, 1978;Kriausakul and Mitterer, 1980 ;Moir and Crawford, 1988) of degrading proteins. In the case of Asx, a decrease in the rate of hydrolysis relative to racemization at higher temperatures will mean increased opportunity for Asx to racemize via (bound) succinimidyl residues prior to hydrolysis to free amino acids.…”

Talaropeptins A and B, Tripeptides with an N-trans-Cinnamoyl Moiety from the Marine-Derived Fungus Talaromyces purpureogenus CX11

“…The absolute configuration of 1 was determined by Marfey's analysis. 13 To avoid epimerization, a particular problem for proline residues, 14 the peptide was hydrolyzed under mild conditions (2 M HCl at 90 °C for 4 h). Derivatization of the hydrolysate with L-FDLA followed by LC−MS analysis in comparison to standards revealed subunits derived from L-Pro and D-Ala in 1 (Figure S1).…”

Efficient Fmoc-Protected Amino Ester Hydrolysis Using Green Calcium(II) Iodide as a Protective Agent

“…Before applying this optimized methodology to most standard amino acids, we investigated the potential racemization of one amino acid, as amino esters are known to epimerize under alkaline conditions [19]. Fmoc-Phe was selected for this assay, as it bears an acidic alpha proton, determined by its high exchange rate [20], is readily separated using Chiralpak AD columns in HPLC experiments [21], and is UV active in its deprotected form.…”