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At least 19 recordsLinked to original sources
PubMed1992

Continuous spectrophotometric assays for beta-glucosidases acting on the plant glucosides L-picein and prunasin.

The neutral pH optimum beta-glucosidases of mammalian liver and almonds are each capable of hydrolyzing a number of plant glucosides, including L-picein (p-hydroxyacetophenone-beta-D-glucoside) and prunasin (D-mandelonitrile-beta-D-glucoside). Taking advantage of the marked differences in the spectra of the substrate/product pairs of L-picein/p-hydroxyacetophenone and prunasin/mandelonitrile, we have devised spectrophotometric assays that permit the continuous monitoring at pH 7.0 of p-hydroxyacetophenone (piceol) release from L-picein by guinea pig hepatic cytosolic beta-glucosidase and mandelonitrile from prunasin by almond beta-glucosidase. When L-picein hydrolysis was monitored at 320 nm and prunasin at 282 nm, the molar absorption coefficients determined for their products, namely piceol and mandelonitrile, were 3200 and 1360 M-1 cm-1, respectively. The kinetic parameter Km and Vmax values obtained using these spectrophotometric procedures for the guinea pig liver cytosolic beta-glucosidase acting on L-picein were 0.88 mM and 5.29 x 10(5) units/mg protein and for the almond beta-glucosidase acting on prunasin, Km 1.1 mM and Vmax 5.24 x 10(6) units/mg protein. These values agreed well with previously reported values obtained using less convenient, discontinuous assay procedures.

Animals↗
PubMed1987

Isolation and characterization of multiple forms of prunasin hydrolase from black cherry (Prunus serotina Ehrh.) seeds.

Three forms of prunasin hydrolase (PH I, PH IIa, and PH IIb), which catalyze the hydrolysis of (R)-prunasin to mandelonitrile and D-glucose, have been purified from homogenates of mature black cherry (Prunus serotina Ehrh.) seeds. Hydroxyapatite chromatography completely resolved PH I from PH IIa and PH IIb. PH IIa and IIb, which coeluted on hydroxyapatite, were resolved by gel filtration. PH IIa was a dimer with a native molecular weight of 140,000. Both PH I and PH IIb were monomeric with molecular weights of 68,000. The isozymes appeared to be glycoproteins based on their binding to concanavalin A-Sepharose 4B with subsequent elution by alpha-methyl-D-glucoside. When presented several potential glycosidic substrates, these enzymes exhibited a narrow specificity towards (R)-prunasin. Km values for (R)-prunasin for PH I, PH IIa, and PH IIb were 1.73, 2.3, and 1.35 mM, respectively. PH I and PH IIb possessed fivefold greater Vmax/Km values than PH IIa. Ortho- and para-nitrophenyl-beta-D-glucosides were hydrolyzed at the same active site. All forms had a pH optimum of 5.0 in citrate-phosphate buffer. PH I and PH IIb were competitively inhibited by castanospermine with Ki values of 0.19 and 0.09 mM, respectively. PH activity was not stimulated by any metal ion tested and was unaffected by diethyldithiocarbamate, o-phenanthroline, 2,2'-dipyridyl, and EDTA.

Chromatography↗
PubMed1982

The pharmacokinetics of prunasin, a metabolite of amygdalin.

The pharmacokinetics of prunasin have been investigated in the dog. The results are compared with results obtained with amygdalin. The volume of distribution and the clearance of prunasin are larger than those of amygdalin. The oral bioavailability of prunasin is approximately 50%, whereas amygdalin is hardly absorbed unchanged.

Administration, Oral↗
PubMed1981

Amygdalin (Laetrile) and prunasin beta-glucosidases: distribution in germ-free rat and in human tumor tissue.

Amygdalin, the gentiobioside derivative of mandelonitrile commonly referred to as Laetrile, is presently under intensive investigation as a potential cancer chemotherapeutic agent. Because of this interest, we investigated the activity of beta-glucosidases that cleave glucose from amygdalin and from prunasin (mandelonitrile monoglucoside) in tissues from germ-free rats and in normal and neoplastic human tissues. Rat and human small intestinal mucosa contain high levels of activity of glucosidases that act on both of these cyanogenic glucosides. Release of glucose from these compounds was not detected in any of the human neoplastic tissues examined in the present study. These observations are consistent with reports of cyanide toxicity through the oral use of amygdalin or prunasin and pose serious questions concerning the alleged tumoricidal effect of amygdalin.

Amygdalin↗
PubMed1986

Intestinal first pass metabolism of amygdalin in the rat in vitro.

The intestinal first pass metabolism of amygdalin has been investigated in rat small intestine in vitro. The results show that amygdalin is hydrolyzed to prunasin, essentially in the wall of the proximal jejunum. This specific beta(1-6)hydrolytic cleavage of the terminal glucose residue is pH-dependent and can be inhibited by glucono-delta-lactone, a potent inhibitor of the lysosomal beta-glucosidase of the rat intestine. No substrate competition between phloridzin and lactose vs amygdalin was noted. None of the more common soluble beta- or alpha-enzymatic activities of mammalian intestine (alpha-glucosidase, alpha-amylase) or mammalian liver (beta-galactosidase, beta-glucuronidase) were capable of catalyzing the hydrolysis of the terminal glucose from amygdalin at pH's 5.0, 7.0 or 9.0. Furthermore, no metabolic activity of isolated rat livers toward amygdalin and prunasin was observed within two hours of recirculating perfusion. However, cecal contents of conventional rats, exhibited both amygdalin- and prunasin-hydrolyzing activities. The resulting mandelonitrile dissociates spontaneously into cyanide and benzaldehyde. Therefore, our findings indicate that metabolism of amygdalin to prunasin occurring in the proximal part of jejunum is apparently mediated by enzymatic beta(1-6)glucosidase activity of the gut wall. In contrast, the toxicity of amygdalin due to the release of cyanide obviously requires microbiological activities of the gut flora.

Amygdalin↗
PubMed1986

Comparison of kinetic and molecular properties of two forms of amygdalin hydrolase from black cherry (Prunus serotina Ehrh.) seeds.

Two forms of the beta-glucosidase amygdalin hydrolase (AH I and II), which catalyze the hydrolysis of (R)-amygdalin to (R)-prunasin and D-glucose, have been purified over 200-fold from mature black cherry (Prunus serotina Ehrh.) seeds. These proteins showed very similar molecular and kinetic properties but could be resolved by chromatofocusing and isoelectric focusing. AH I and II were monomeric (Mr 60,000) and had isoelectric points of 6.6 and 6.5, respectively. Their glycoprotein character was indicated by positive periodic acid-Schiff staining and by their binding to concanavalin A-Sepharose 4B with subsequent elution by alpha-Me-D-glucoside. Of the natural glycosidic substrates tested, both enzymes showed a pronounced preference for the endogenous cyanogenic disaccharide (R)-amygdalin. They also hydrolyzed at the same active site the synthetic substrates p-nitrophenyl-beta-D-glucoside and 4-methylumbelliferyl-beta-D-glucoside but were inactive towards (R)-prunasin, p-nitrophenyl-alpha-D-glucoside, and 4-methylumbelliferyl-alpha-D-glucoside. Maximum hydrolytic activity was shown in citrate-phosphate buffer in the pH range 4.5-5.0. AH I and II were inhibited competitively by the reaction product (R)-prunasin and noncompetitively (mixed type) by delta-gluconolactone and castanospermine.

Chemical Phenomena↗
PubMed1986

Comparative metabolism of linamarin and amygdalin in hamsters.

Rates of cyanide liberation resulting from hydrolysis of the cyanogenic glycosides linamarin, amygdalin and prunasin by a crude beta-glucosidase prepared from hamster caecum were studied in vitro. In addition, hamster blood cyanide and thiocyanate concentrations were determined at 0.5, 1, 2, 3 and 4 hr after an oral dose of 0.44 mmol linamarin or amygdalin/kg body weight. Plots of cyanide liberated v. time for linamarin and prunasin yielded straight lines. A similar plot for amygdalin was curvilinear, with the rate of cyanide release increasing with time. At 10(-3) M substrate concentrations, the average rates of hydrolysis of prunasin, amygdalin and linamarin were 1.39, 0.57 and 0.13 nmol/min/mg protein, respectively. Lineweaver-Burk plots yielded apparent Km and Vmax values of 3.63 X 10(-5) M and 0.35 nmol/min/mg protein, respectively, for amygdalin, and 7.33 X 10(-3) M and 1.04 nmol/min/mg protein, respectively, for linamarin. Blood cyanide concentrations following amygdalin treatment reached their highest level (130 nmol/ml) 1 hr after dosing and remained elevated until 3 hr after treatment. Blood cyanide concentrations following linamarin treatment reached their highest level (116 nmol/ml) after 3 hr and then declined immediately. Area under the blood cyanide concentration-time curve was 395 nmol-hr/ml for amygdalin and 318 nmol-hr/ml for linamarin. The results suggest a faster rate of enzymatic hydrolysis and cyanide absorption for amygdalin than for linamarin.

Amygdalin↗
PubMed1967

The enzymic hydrolysis of amygdalin.

Chromatographic examination has shown that the enzymic hydrolysis of amygdalin by an almond beta-glucosidase preparation proceeds consecutively: amygdalin was hydrolysed to prunasin and glucose; prunasin to mandelonitrile and glucose; mandelonitrile to benzaldehyde and hydrocyanic acid. Gentiobiose was not formed during the enzymic hydrolysis. The kinetics of the production of mandelonitrile and hydrocyanic acid from amygdalin by the action of the beta-glucosidase preparation favour the probability that three different enzymes are involved, each specific for one hydrolytic stage, namely, amygdalin lyase, prunasin lyase and hydroxynitrile lyase. Cellulose acetate electrophoresis of the enzyme preparation showed that it contained a number of enzymically active components.

Aldehydes↗
PubMed1985

On the metabolism of amygdalin. 2. The distribution of beta-glucosidase activity and orally administered amygdalin in rats.

The organs of 15-day-old rats had the highest capability to hydrolyze amygdalin and prunasin, and most of this activity is concentrated in the tissues of the small and large intestines. The activity decreased with age. In adult rats, the ability of the organs to hydrolyze prunasin is higher than that of amygdalin and is concentrated in the spleen, large intestine, and kidney (35.0, 15.0, and 8.9 micrograms prunasin hydrolyzed . h-1 . g tissue-1). Minced tissues of the liver, spleen, kidney, and stomach contain more hydrolytic capability than the homogenate of these organs, while the reverse is the case with the small and large intestines. When 30 mg amygdalin was orally administered to adult rats, its distribution after the 1st h was as follows: stomach (0.89 mg), small intestine (0.78 mg), spleen (0.36 mg), large intestine (0.30 mg), kidney (0.19 mg), liver (0.10 mg), and serum (5.6 micrograms/mL). At the end of the 2nd h, the highest amygdalin content was found in the large intestine (0.79 mg).

Administration, Oral↗
PubMed1992

Exolytic hydrolysis of toxic plant glucosides by guinea pig liver cytosolic beta-glucosidase.

We demonstrate that although the guinea pig liver cytosolic beta-glucosidase does not catalyze the hydrolysis of gentiobiose, it does hydrolyze, disaccharide-containing glycosides such as p-nitrophenyl-beta-D-gentiobioside (Glc beta 1----6Glc beta-pNP) and mandelonitrile-beta-D-gentiobioside (amygdalin). Furthermore, we establish that the enzyme attacks disaccharide glycosides exolytically; specifically, we document the exolytic deglucosylation of amygdalin and the generation of the intermediate monosaccharide glycoside mandelonitrile-beta-D-glucoside prior to the formation of the aglycone (mandelonitrile). We also show that the cytosolic beta-glucosidase catalyzes the hydrolysis of various phenolic (e.g. arbutin and salicin) and cyanogenic plant glucosides (e.g. prunasin). Using the everted gut-sack technique, we demonstrate that the plant glucosides, amygdalin, prunasin, and vicine, are transported across the small intestine of the guinea pig efficiently and without being hydrolyzed. Based on these data we speculate that the cytosolic beta-glucosidase may participate in biotransformation of toxic plant glucosides.

Amygdalin↗
PubMed2025

Indel mutation in transcription factor PabHLH2 regulates amygdalin accumulation and kernel bitterness in apricot.

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.

Amygdalin↗
PubMed1988

Cyanogenesis and the role of cyanogenic compounds in insects.

The cyanogenic system comprising cyanogenic glycosides, hydroxynitriles (cyanohydrins), beta-glucosidases and nitrile lyases is widespread in the plant kingdom but also occurs in several arthropods. A few insects were found to contain mandelonitrile and, in one case, a small amount of prunasin was detected. Cardiospermin and gynocardin occur in one insect, and the cyanoglucosides linamarin and lotaustralin are found in several species of the lepidopterans. Biosynthesis of these cyanoglucosides has been studied in two of these species and their sequestration has been investigated in one species. For Zygaena trifolii the presence of the entire cyanide-handling system indicates an important function of these compounds. So far, their function as defensive compounds seems likely on the basis of their ability to generate HCN and their localization, and appears to be indicated by some feeding experiments with potential predators.

Animals↗
PubMed1982

The pharmacokinetics of amygdalin.

Amygdalin (D-mandelonitrile-beta-D-gentiobioside) is a cyanogenic glycoside claimed to show anti-cancer activity, sold under the incorrect name "Laetrile". For a sensible discussion of its alleged activity and its established toxicity it is necessary that its fate in the organism is known. The pharmacokinetics of amygdalin have been investigated in the Beagle dog after both intravenous and oral administration. The excretion of amygdalin has also been studied in the rat. Amygdalin concentrations were determined by high performance liquid chromatography in plasma ultrafiltrate and urine. The pharmacokinetics of amygdalin after intravenous administration were compared with those of diatrizoate, a model substance for extracellular volume and glomerular filtration. The amygdalin clearance is significantly larger than that of diatrizoate. The volumes of distribution of both substance are the same. After oral administration only a few percents of the amygdalin dose are systemically available. A part of the oral dose is recovered from the urine as prunasin (D-mandelonitrile-beta-D-glucoside).

Administration, Oral↗
PubMed1971

Oximes, nitriles and 2-hydroxynitriles as precursors in the biosynthesis of cyanogenic glucosides.

The biosynthesis of the cyanogenic glucosides, linamarin and prunasin, was investigated in linen-flax, peach and cherry-laurel shoots. It was shown that related 2-oximino acids, aldoximes, nitriles and 2-hydroxynitriles were generally good precursors of the aglycone moiety. Studies with double-labelled compounds confirmed the retention of the oximino nitrogen atom from 2-oximinoisovaleric acid and isobutyraldoxime in the biosynthesis of linamarin. A general pathway from amino acids to cyanogenic glucosides involving N-hydroxyamino acids, aldoximes, nitriles and 2-hydroxynitriles is proposed.

Aldehydes↗
PubMed1987

Purification and properties of beta-D-glucosidase (linamarase) from the butter bean, Phaseolus lunatus.

A beta-D-glucosidase (linamarase) was purified 11,700-fold from the butter bean, Phaseolus lunatus L., by means of successive procedures including extraction, ammonium sulfate fractionation, acetone treatment, and chromatographies on CM-Sephadex, DEAE-Sephadex, and Sephadex G-200. The final preparation gave a single protein band on both disc polyacrylamide gel electrophoresis and SDS-polyacrylamide gel electrophoresis. In spite of its electrophoretic purity, the final enzyme preparation showed four glycosidase activities; beta-D-glucosidase, beta-D-galactosidase, beta-D-fucosidase, and beta-D-xylosidase. The molecular weight of the enzyme was determined to be 124,000 +/- 9,000 by Sephadex G-200 gel filtration, and 59,000 +/- 2,400 by SDS-disc gel electrophoresis. The enzyme showed a pH optimum in the range of 5.1 to 6.0 with p-nitrophenyl beta-D-glucoside, 4-methylumbelliferyl beta-D-glucoside, and linamarin. Among natural substrates containing a beta-glucosyl terminal, linamarin, prunasin, and salicin were hydrolyzed by the enzyme from butter beans, but amygdalin, cellobiose, gentiobiose, and laminarin were hardly hydrolyzed.

Amino Acids↗
PubMed1990

Factors that determine rates of cyanogenesis in bovine ruminal fluid in vitro.

Strained ruminal fluid was collected from cattle fed five diets at two locations to determine in vitro rates of cyanogenesis from the glycosides amygdalin, prunasin and linamarin. Rates of dissociation for the corresponding aglycones, benzaldehyde cyanohydrin and acetone cyanohydrin, also were determined. Hydrogen cyanide (HCN) in ruminal fluid was determined with a modified method of HCN analysis that independently measured the overall rate of cyanogenesis and the nonenzymatic dissociation of cyanohydrins, the intermediate products in the degradation of cyanogenic glycosides to HCN. Rate of dissociation of cyanohydrins in ruminal fluid was pH-dependent, with high rates of dissociation (as expressed by the rate constant or half-life of the reaction) occurring at pH greater than 6 and slower rates at pH 5 to 6. Cyanohydrin dissociation was most rapid when cattle were fasted for 24 to 48 h and ruminal pH was high; rate of dissociation was much slower during feeding and digestion. When the glycosides were examined, highest rates of cyanogenesis (mg HCN.liter-1.s-1) were observed after a 24-h postprandial period. Hence, cattle are most susceptible to poisoning by cyanogenic plants when the pH of ruminal fluid is elevated (for rapid dissociation) and also when the activity of microbial beta-glucosidase is adequate for rapid hydrolysis of glycosidic bonds. Rates of cyanogenesis were higher when ruminal inocula were from cattle fed fresh alfalfa or cubed alfalfa hay rather than grain or long hay. Rates of HCN production were slowest using inocula from cattle fed grain; rates for the three glycosides were negligible at the 3 and 6 h postprandial sampling times.(ABSTRACT TRUNCATED AT 250 WORDS)

Amygdalin↗