The biosynthesis of -amyrin and -sitosterol in germinating seeds of Pisum sativum

Baisted, D.J.; Capstack, E.; Nes, W.R.

Biochemistry 1(3): 537-541


ISSN/ISBN: 0006-2960
DOI: 10.1021/bi00909a027
Accession: 025692024

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As part of a study of biosynthetic sequences in immature tissues which has been designed to approach the problem of evolution from the standpoint of ontogenetic recapitulation of phylogenesis, we have investigated the biosynthesis of isopentenoids in germinating seeds of the pea, Pisum sativum. During a 5-day period radioactivity from 2-C14-mevalonic acid was incorporated into ii-amyrin to an extent of 45% and into β-sitosterol to an extent of only 2.2%. The possibility is raised that this difference in apparent rates of formation results from the fact that β-amyrin arises immediately by the complete cyclization of squalene, whereas β-sitosterol is formed by the longer and more complicated process of partial cyclization of squalene, external alkylation and reduction of the terminal double bond, removal of three methyl groups, and changes in the unsaturation of ring-B.