The Use of Cell-Free Systems in Studies of Carotenoid Biosynthesis

Abstract

A perusal of the literature on carotenoid biosynthesis reveals that over 25 different cell-free systems have been reported to synthesise carotenoids in vitro ¹. Typical examples from higher plants, fungi and prokaryotes are listed in Table 1. In general, the most active preparations from higher plants are derived from chromoplasts, e.g. Narcissus flowers and and tomato and Capsicum fruits. Chloroplast systems have been notoriously poor at metabolising phytoene, but a recent report of an active preparation from Zea mays ⁷ indicates that enzymological studies with chloroplasts may soon be possible. The fungal cell extracts vary in their abilities to produce unsaturation carotenoids, with those from Phycomyces and Aspergillus exhibiting some of the highest carotenogenic activities. Thylakoids from the cyanobacterium Aphanocapsa shows similar rates of β-carotene formation, and can also produce xanthophylls (Fig. 2). The cell extract of Flavobacterium has recently been used in the conversion of d₆-lycopene into β-carotene¹⁴.