PubMed · 375560
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1979. Laetrile bibliography.. https://pubmed.ncbi.nlm.nih.gov/375560/
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Amygdalin, the phytochemical responsible for the characteristic bitterness of apricot (Prunus armeniaca L.) kernels, also exhibits significant bioactive properties and therapeutic potential. Genetic regulation of amygdalin content is therefore a key objective in apricot breeding programs aimed at quality improvement. In this study, we conducted quantitative trait loci (QTL) mapping to uncover the genetic basis of sweet-bitter differentiation in apricot kernels. We identified a 15-bp insertion/deletion (indel) polymorphism strongly related to kernel bitterness, with marker validation achieving 100% concordance across 601 apricot germplasm accessions. Notably, this polymorphic site is located within the helix-loop-helix (HLH) domain of the basic HLH (bHLH) transcription factor PabHLH2. Protein interaction analyses revealed that the 15-bp deletion variant impaired dimerization capacity, reducing transcriptional activation of downstream targets. Using yeast one-hybrid screening and dual-luciferase reporter assays, we identified PaCYP71AN24 and PaCYP79D16 as direct transcriptional targets of PabHLH2. Functional characterization further indicated that the PabHLH2a variant (harboring the 15-bp insertion) significantly enhanced the promoter activity of these cytochrome P450 genes compared with the deletion variant. Transient overexpression and silencing experiments in apricot kernels further confirmed that the 15-bp insertion positively regulates both PaCYP71AN24/PaCYP79D16 expression and prunasin accumulation, the immediate biosynthetic precursor of amygdalin. Overall, these findings provide mechanistic insights into the allelic variation underlying kernel bitterness and delineate the molecular cascade of amygdalin biosynthesis. The identified molecular markers and functional characterization establish a basis for marker-assisted breeding of low-amygdalin apricot cultivars, supporting the dual-purpose utilization of kernels in food and pharmaceutical industries.
The separation of amygdalin, prunasin and their isomers neoamygdalin and sambunigrin could be achieved with micellar capillary electrophoresis (MEKC). The two isomers were obtained in alkaline conditions and were produced in less than 15 min at pH 11.0. The developed methods showed a good selectivity in the separation of the isomers only in the presence of SDS micelles. The working pH was optimized to allow best resolution and quantitative analysis of these compounds. With a linear calibration over an injection time from 1 to 20 s, the detection limit was found to be in the range of 5 microM (S/N=3; 20 s injection time). Two pH buffer systems (pH 5.2 and pH 9.1) were chosen to confirm the peak attributions of the compounds in the apple and peach seeds samples. Sambunigrin was found in both apple and peach seeds but could not be quantified because of missing standards. Prunasin and amygdalin were not found in the apple sample, while they were quantified in the peach seeds in concentrations of 50 microg/g and 90 microg/g (dry weight), respectively.
We have developed a simple, rapid and reproducible method for the determination of D-amygdalin and its epimer by using micellar electrokinetic chromatography (MEKC). Separation of D-amygdalin was performed in a 20 mM sodium borate buffer (pH 8.5) containing 300 mM sodium dodecyl sulfate using a bare fused-silica capillary. The eluates were monitored by the absorbance at 210 nm. The applied electric field was 278 V/cm, and the time needed for the separation of D-amygdalin did not exceed 6 min. The calibration curve for D-amygdalin showed excellent linearity in the concentration range of 5-500 microg/ml. The migration time and the corrected peak area show relative standard deviations (n=6) of 0.86% and 1.48%, respectively. The limit of detection (S/N=3) for D-amygdalin was 2 microg/ml. Under acidic and neutral conditions, amygdalin exists only as the D-form; however, under basic conditions, it shows both the D- and L-forms with a concentration ratio of 1:1.3 (D-amygdalin/L-amygdalin). Results of HPLC, UV-Vis spectrophotometry, and mass spectrometry reconfirmed the identification of D-amygdalin and its epimer. The number of theoretical plates of D-amygdalin is about 100,000 in MEKC, which is significantly higher than approximately 8,000 of HPLC. This method has been successfully applied to the determination of amygdalin epimers in various apricot kernel extracts and pharmaceutical products.