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A dual positional specific lipoxygenase functions in the generation of flavor compounds during climacteric ripening of apple.

Schiller D, Contreras C, Vogt J, Dunemann F, Defilippi BG, Beaudry R, Schwab W - Hortic Res (2015)

Bottom Line: Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation.The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples.While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

View Article: PubMed Central - PubMed

Affiliation: Biotechnology of Natural Products, Technische Universität München , Liesel-Beckmann-Str. 1, D-85354 Freising, Germany.

ABSTRACT
Lipoxygenase (LOX) is an important contributor to the formation of aroma-active C6 aldehydes in apple (Malus × domestica) fruit upon tissue disruption but little is known about its role in autonomously produced aroma volatiles from intact tissue. We explored the expression of 22 putative LOX genes in apple throughout ripening, but only six LOXs were expressed in a ripening-dependent manner. Recombinant LOX1:Md:1a, LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b proteins showed 13/9-LOX, 9-LOX, 13/9-LOX and 13-LOX activity with linoleic acid, respectively. While products of LOX1:Md:1c and LOX2:Md:2b were S-configured, LOX1:Md:1a and LOX2:Md:2a formed 13(R)-hydroperoxides as major products. Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation. The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples. While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

No MeSH data available.


Proposed metabolism of fatty acids in the intact apple fruit. Saturated and mono-saturated fatty acids are degraded to precursor molecules for straight-chain esters via β-oxidation. For PUFAs, this process seems to be partially impaired. Precursors for straight chain esters might be formed via the action of the LOX pathway, instead. PUFA, polyunsaturated fatty acid.
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fig7: Proposed metabolism of fatty acids in the intact apple fruit. Saturated and mono-saturated fatty acids are degraded to precursor molecules for straight-chain esters via β-oxidation. For PUFAs, this process seems to be partially impaired. Precursors for straight chain esters might be formed via the action of the LOX pathway, instead. PUFA, polyunsaturated fatty acid.

Mentions: We propose that MdLOX1a is responsible for the majority of LOX activity found in intact apple fruits during the late stages of the ripening process based, among others, on the peculiar conformity of the regio- and stereochemistry of the hydroperoxide products formed by the recombinant and endogenous enzyme. Thus, LOX1:Md:1a is suggested to be involved in the generation of C6 aldehydes (primarily hexanal in the case of apple) and the formation of hexyl and possibly other straight-chain esters in intact, ripening fruit (Figure 7) whereas other LOXs primarily take part in the production of ‘green note’ aldehydes. In particular, the coincident ripening-dependent decline in the synthesis of unsaturated C6 aldehydes in disrupted tissue and associated esters7 and the decline in two of the putative 13-LOX genes, MdLOX6a and MdLOX6b, reported herein is also suggestive of the involvement of specific LOX genes in regulating the synthesis of disruption-dependent aldehydes.


A dual positional specific lipoxygenase functions in the generation of flavor compounds during climacteric ripening of apple.

Schiller D, Contreras C, Vogt J, Dunemann F, Defilippi BG, Beaudry R, Schwab W - Hortic Res (2015)

Proposed metabolism of fatty acids in the intact apple fruit. Saturated and mono-saturated fatty acids are degraded to precursor molecules for straight-chain esters via β-oxidation. For PUFAs, this process seems to be partially impaired. Precursors for straight chain esters might be formed via the action of the LOX pathway, instead. PUFA, polyunsaturated fatty acid.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595979&req=5

fig7: Proposed metabolism of fatty acids in the intact apple fruit. Saturated and mono-saturated fatty acids are degraded to precursor molecules for straight-chain esters via β-oxidation. For PUFAs, this process seems to be partially impaired. Precursors for straight chain esters might be formed via the action of the LOX pathway, instead. PUFA, polyunsaturated fatty acid.
Mentions: We propose that MdLOX1a is responsible for the majority of LOX activity found in intact apple fruits during the late stages of the ripening process based, among others, on the peculiar conformity of the regio- and stereochemistry of the hydroperoxide products formed by the recombinant and endogenous enzyme. Thus, LOX1:Md:1a is suggested to be involved in the generation of C6 aldehydes (primarily hexanal in the case of apple) and the formation of hexyl and possibly other straight-chain esters in intact, ripening fruit (Figure 7) whereas other LOXs primarily take part in the production of ‘green note’ aldehydes. In particular, the coincident ripening-dependent decline in the synthesis of unsaturated C6 aldehydes in disrupted tissue and associated esters7 and the decline in two of the putative 13-LOX genes, MdLOX6a and MdLOX6b, reported herein is also suggestive of the involvement of specific LOX genes in regulating the synthesis of disruption-dependent aldehydes.

Bottom Line: Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation.The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples.While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

View Article: PubMed Central - PubMed

Affiliation: Biotechnology of Natural Products, Technische Universität München , Liesel-Beckmann-Str. 1, D-85354 Freising, Germany.

ABSTRACT
Lipoxygenase (LOX) is an important contributor to the formation of aroma-active C6 aldehydes in apple (Malus × domestica) fruit upon tissue disruption but little is known about its role in autonomously produced aroma volatiles from intact tissue. We explored the expression of 22 putative LOX genes in apple throughout ripening, but only six LOXs were expressed in a ripening-dependent manner. Recombinant LOX1:Md:1a, LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b proteins showed 13/9-LOX, 9-LOX, 13/9-LOX and 13-LOX activity with linoleic acid, respectively. While products of LOX1:Md:1c and LOX2:Md:2b were S-configured, LOX1:Md:1a and LOX2:Md:2a formed 13(R)-hydroperoxides as major products. Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation. The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples. While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

No MeSH data available.