What Is 2-hydroxyisoflavanone synthase

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Last updated: April 15, 2026

Quick Answer: 2-Hydroxyisoflavanone synthase (2-HIS) is a plant-specific cytochrome P450 enzyme (CYP93C subfamily) that catalyzes the conversion of flavanones to 2-hydroxyisoflavanones, a key step in isoflavonoid biosynthesis. This reaction occurs in leguminous plants such as soybean and alfalfa, primarily between 1985 and 1990 when the enzyme was first isolated and characterized.

Key Facts

2-Hydroxyisoflavanone synthase belongs to the CYP93C subfamily of cytochrome P450 enzymes
It catalyzes the aryl migration of flavanones to form 2-hydroxyisoflavanones
The enzyme was first isolated in 1988 from soybean (Glycine max)
Reaction occurs at the endoplasmic reticulum membrane in plant cells
Essential for producing phytoalexins and antioxidant isoflavonoids in legumes

Overview

2-Hydroxyisoflavanone synthase (2-HIS) is a critical enzyme in the biosynthesis of isoflavonoids, a class of plant secondary metabolites primarily found in legumes. These compounds play essential roles in plant defense mechanisms and have significant implications for human health due to their antioxidant and phytoestrogenic properties.

The enzyme functions at a pivotal branch point in the phenylpropanoid pathway, directing metabolic flux toward isoflavonoid production rather than flavonoids. This specificity makes 2-HIS a key target for metabolic engineering in crops like soybean and red clover.

Substrate specificity: 2-HIS exclusively acts on flavanones such as naringenin and liquiritigenin, converting them into corresponding 2-hydroxyisoflavanones through a unique aryl migration mechanism.
Enzyme classification: It is a member of the cytochrome P450 superfamily, specifically designated as CYP93C, distinguishing it from other P450 enzymes involved in flavonoid metabolism.
Cellular location: The enzyme is anchored in the endoplasmic reticulum membrane of plant cells, where it interacts with NADPH-dependent cytochrome P450 reductase for electron transfer.
Discovery timeline: First purified in 1988 from Glycine max (soybean), marking a breakthrough in understanding legume-specific secondary metabolism.
pH optimum: The enzyme exhibits maximal activity at pH 7.5–8.0, indicating a preference for slightly alkaline intracellular environments in planta.

How It Works

2-Hydroxyisoflavanone synthase catalyzes a two-step oxidative reaction involving aryl migration and hydroxylation, forming the core structure of isoflavonoids essential for plant defense and signaling.

Aryl migration:The enzyme facilitates a 1,2-shift of the B-ring from C2 to C3 of the flavanone skeleton, a rare biochemical rearrangement that defines isoflavonoid biosynthesis.
Oxidation mechanism: It performs three successive monooxygenase reactions using molecular oxygen and NADPH, ultimately producing 2-hydroxyisoflavanone as an unstable intermediate.
Dehydration step: The 2-hydroxyisoflavanone product spontaneously dehydrates to form stable isoflavones like daidzein and genistein, major isoflavones in soy products.
Gene expression:CYP93C genes are induced by pathogen attack or elicitors such as jasmonic acid, linking enzyme activity to plant immune responses.
Kinetic parameters: Purified 2-HIS shows a Km of ~5 μM for naringenin and a turnover number (kcat) of approximately 0.8 min⁻¹ in recombinant systems.
Evolutionary origin: The enzyme evolved specifically in legume lineages around 50–60 million years ago, coinciding with the diversification of nitrogen-fixing symbioses.

Comparison at a Glance

Below is a comparison of 2-hydroxyisoflavanone synthase with related enzymes in flavonoid biosynthesis:

Enzyme	EC Number	Reaction Type	Product	Found In
2-Hydroxyisoflavanone synthase	EC 1.14.14.86	Aryl migration + hydroxylation	2-Hydroxyisoflavanone	Legumes (e.g., soybean)
Flavanone 3-hydroxylase	EC 1.14.11.9	Hydroxylation	Dihydrokaempferol	Most plants
Chalcone isomerase	EC 5.5.1.6	Isomerization	Naringenin	Wide distribution
Isoflavone synthase	EC 1.14.14.86	Synonym for 2-HIS	Daidzein precursor	Legumes only
Flavone synthase I	EC 1.14.14.106	Desaturation	Apigenin	Apiaceae family

This table highlights the uniqueness of 2-HIS in catalyzing aryl migration, a reaction absent in most other plant lineages. Its restriction to legumes underscores the evolutionary adaptation for symbiotic nitrogen fixation and pathogen resistance.

Why It Matters

Understanding 2-hydroxyisoflavanone synthase has far-reaching implications for agriculture, nutrition, and pharmaceutical development. Its role in producing bioactive compounds makes it a focal point for biotechnological innovation.

Disease resistance: Plants with upregulated 2-HIS expression show enhanced resistance to fungal pathogens like Phytophthora sojae due to increased phytoalexin production.
Nutritional enhancement: Metabolic engineering of this enzyme can boost isoflavone content in crops, improving the health benefits of soy-based foods.
Pharmaceutical relevance: Isoflavones derived from 2-HIS activity are studied for anti-cancer and estrogenic effects in humans, particularly in hormone-related conditions.
Gene editing target: CRISPR-Cas9 has been used to modify CYP93C genes in model legumes to study isoflavonoid function and optimize yield.
Environmental adaptation: The enzyme's induction under stress suggests potential for developing climate-resilient crops with improved secondary metabolism.
Biotechnological applications: Heterologous expression of 2-HIS in yeast or tobacco enables sustainable production of medicinal isoflavonoids without field cultivation.

As research advances, 2-hydroxyisoflavanone synthase continues to emerge as a cornerstone in plant biochemistry, bridging ecological adaptation with human health applications.