Identification of an isoflavone glycoside hydrolyzing b-glucosidase in the seeds of the desert legume Prosopis cineraria

Abstract

Legumes, in general, are rich in glycosidic isoflavone conjugates, whereby specific -glucosidases act to release the free aglycones that could serve in plant-microbe interactions and defense. Prosopis cineraria is an important legume tree, bearing medicinally useful and edible pods, generally growing in extreme arid/semi-arid zones of Rajasthan. However, specific phytochemical-cum-metabolic profiles are lacking for the same. Therefore, the present investigation undertook phytochemical and metabolic screening of the pods/seeds of P. cineraria for the presence of putative isoflavonoids viz. genistein and daidzein, their glycosides and -glucosidase(s) capable of catalyzing the glycoside hydrolysis. Extraction and identification of these two aglycone forms of the above isoflavonoids were performed with solvent partition chromatography and Fluorescent/High Performance Thin Layer Chromatography, respectively. Furthermore, optimization of the isoflavone conjugate-specific -glucosidase activity with respect to pH optima, temperature and time were carried out. The partially purified enzyme showed a temperature optima of 50°C and pH optima of 4.5. The enzyme also demonstrated activity towards natural substrates daidzin and genistin which are glycosides of isoflavonoids daidzein and genistein respectively. The methanolic extracts of the seeds of P. cineraria indicated the presence of related isoflavonoids which needs to be further validated.

Nature-inspired Enzyme engineering and sustainable catalysis: biochemical clues from the world of plants and extremophiles

“…It has been reported that the desert legumes such as Prosopis cineraria and Cyamopsis tetragonoloba harbor thermostable β-glucosidase enzymes (EC 3.2.1.21), capable of showing significant catalytic activity even above 50°C temperature (V Asati & Sharma, 2018 ; Asati and Sharma, 2019 ). These enzymes were specific towards isoflavone glycosides and did not show any activity with glycosides of other flavonoid categories, possibly due to difference in structure of the substrate, that is, flavonoid parent skeleton (benzene ring connected to Carbon 3 of C-ring in case of isoflavonoids, as against Carbon 2 in case of flavonoids).…”

Desert legume Prosopis cineraria as a novel source of antioxidant flavonoids / isoflavonoids: Biochemical characterization of edible pods for potential functional food development

“…The commercial importance of food-based antioxidants is increasingly being realized, as exemplified by research on various plants including legumes, primarily due to the toxicity of synthetic antioxidants to humans [ 3 ]. Interestingly, many of these antioxidants such as flavonoids are stored in the plant cell's vacuole in glycosylated forms, which are acted upon by specific β-glucosidases to make the more active aglycone available to the plant [ 4 ]. On a more commercial forefront, Mai et al [ 5 ] have recently characterized a β-glucosidase from mangrove sediments, showing high catalytic activity on soy isoflavone glycosides.…”