Biosynthesis of α-Tocopherol and Plastoquinone-9 in spinach chloroplasts

Prenylation and methylation reaction in al biosynthesis is localized in the envelope membranes of the chloroplasts, while PQ-9 biosynthesis takes place in the envelope membranes and also in the thylakoid membranes. The sequence in a-T biosynthesis in spinach is (see also Figure 1): Homogentisate + Phytyl-PP —> Me-6-PQH?—> 2,3-Me2PQH?—>γ J ->a T ; for the PQ-9 biosynthesis it is: Homogentisate + Solanesyf-PP4-> Me-6-SQH2—> PQH2

Comparison of geranylgeranyl and phytyl substituted methylquinols in the tocopherol synthesis of spinach chloroplasts

Geranylgeranyl substituted methylquinols are shown to be precursors of tocopherol biosynthesis in spinach chloroplasts as well as phytyl substituted ones. The geranylgeranyl substituted quinols are methylated even to a greater extent than the phytyl substituted ones. The connection to the so far known biosynthetic origin of -tocopherol is probably -tocotrienol which is hydrogenated to γ-tocopherol and then further methylated to -tocopherol

2-Methyl-6-phytylquinol and 2,3-dimethyl-5-phytylquinol as precursors of tocopherol synthesis in spinach chloroplasts

The incorporation of [Me-14C] from SAM-[Me-14C] into precursors indicates the following sequence of tocopherol synthesis in spinach: 2-methyl-6-phytylquinol (6-phytyltoluquinol) (1a) → 2,3-dimethyl-5-phytylquinol (phytylplastoquinol) (2a)→,γ-tocopherol (5a)→-tocopherol (6). 1a is particularly preferred to 2-methyl-5-phytylquinol (1b) and 2-methyl-3-phytylquinol (1c). 1a only forms 2a. 2a is converted to 6 via 5a and, to a lesser extent, 2,5-dimethyl-6-phylquinol (2b) to 6 via β-tocopherol (5b). Trimethylphytylquinol (3) is not an intermediate in the formation of 6. All reactions are independent of light

Site of biosynthesis of a-tocopherol in spinach chloroplasts

The chloroplast envelope is a continuous boundary of two osmiophilic membranes and has an important role in galactolipid synthesis [ 11. It was interesting to determine whether the envelope is the site of synthesi

Site of methylation of 2-phytyl-1,4-naphthoquinol in phylloquinone (vitamin K1) synthesis in spinach chloroplasts

Phylloquinol (the quinol form of vitamin K1) is synthesized from 2-phytyl-1,4-naphthoquinol and S-adenosylmethionine at the thylakoid membranes of spinach chloroplasts. The addition of soluble stroma protein (chloroplast extract) is necessary S-Adenosylhomocysteine acts as strong competitive inhibitor