The synthesis of (S)-beta-macrocarpene from (2E,6E)-farnesyl diphosphate proceeds in two steps. The first step is the cyclization to (S)-beta-bisabolene (cf. EC 4.2.3.55, (S)-beta-bisabolene synthase). The second step is the isomerization to (S)-beta-macrocarpene.
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The expected taxonomic range for this enzyme is: Zea mays
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SYSTEMATIC NAME
IUBMB Comments
(S)-beta-macrocarpene lyase (decyclizing)
The synthesis of (S)-beta-macrocarpene from (2E,6E)-farnesyl diphosphate proceeds in two steps. The first step is the cyclization to (S)-beta-bisabolene (cf. EC 4.2.3.55, (S)-beta-bisabolene synthase). The second step is the isomerization to (S)-beta-macrocarpene.
in the presence of geranylgeranyl diphosphate, TPS11 also catalyzes the formation of beta-myrcene and linalool, along with minor amounts of limonene, alpha-thujene, sabinene, and alpha-terpinolene
the synthesis of (S)-macrocarpene from (2E,6E)-farnesyl diphosphate in two steps. The first step is the cyclization to (S)-beta-. The second step is the isomerization to (S)-beta-macrocarpene ((S)-beta-macrocarpene synthase)
TPS6 requires a divalent metal ion, with Mg2+ and Mn2+ being effective, optimum activity with 5 mM Mg2+ and 5 mM Mn2+. Although the Km for Mn2+ is significantly lower than for Mg2+, the enzyme is more likely to operate with a Mg2+ cofactor in planta, because the concentration of Mg2+ in plant cells is about 2 orders of magnitudes higher than Mn2+. In the presence of Mn2+, the product spectrum of TPS6 is shifted toward an increased production of (S)-beta-bisabolene and a decreased production of (S)-beta-macrocarpene. KM-value for Mg2+ measured with 0.01 mM farnesyl diphosphate: 0.131 mM
TPS6 requires a divalent metal ion, with Mg2+ and Mn2+ being effective, optimum activity with 5 mM Mg2+ and 5 mM Mn2+. Although the Km for Mn2+ is significantly lower than for Mg2+, the enzyme is more likely to operate with a Mg2+ cofactor in planta, because the concentration of Mg2+ in plant cells is about 2 orders of magnitudes higher than Mn2+. In the presence of Mn2+, the product spectrum of TPS6 is shifted toward an increased production of (S)-beta-bisabolene and a decreased production of (S)-beta-macrocarpene. KM-value for Mn2+ measured with 0.01 mM farnesyl diphosphate: 0.0234 mM
half-maximal activity at pH 6.2 and at pH 8.6, in presence of 5 mM Mg2+. Within a pH range from 5.0 to 8.0, the major product is (S)-beta-macrocarpene, but higher pH values favor the formation of (S)-beta-bisabolene
Protonation of a neutral (S)-beta-bisabolene intermediate is involved in (S)-beta-macrocarpene formation by the maize sesquiterpene synthases TPS6 and TPS11
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5.5.1.17 (S)-beta-macrocarpene synthase
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