Chlorophyll synthetase

Shcherbakov, R.A. and N.V. Shalygo Determination of chlorophyll synthetase activity in green tobacco leaves using exogenous Zn-chlorophyllide a J. Appl. Spectroscopy 73 (2006) 103-106. 

The final step in the biosynthetic pathway to chlorophylls is the esterification of the chlorophyllides with phytyl diphosphate or geranylgeranyl diphosphate (followed by reduction of the three extra double bonds) via the enzyme chlorophyll synthetase. Once again, when zinc or cadmium replaces magnesium, esterification is unaffected. However, when nickel or copper are used, esterification is hindered. Presumably the labile coordinating power of the group Ila and Ilb metals, as opposed to the more inert coordination of transition metals, is involved in the function of the two enzymes, oxidative cyclase and chlorophyll synthetase. 

Gaubler P, Wu HI, Laudie M, Delseny M, Grellet E. A chlorophyll synthetase gene from Arabidopsis thaliana. Mol Gen Genet. 1995 249 58-64. 

The effect of chelators in the light is known to inhibit chlorophyll synthesis (5). We corroborate and extent the observation of (9) that one possible site of inhibition of chlorophyll synthesis is the esterification of chlide. We do not agree, however, with (9) that chloro-phyllase is the attacked enzyme. According to (11), chlorophyll synthetase is responsible for phytylation of chlide. Here we report the first evidence that esterification of chlide is a real target of metal chelator action. 

In summary, treatment of cress seedlings with chelators leads to increased accumulation of chlorophyll precursors in the dark, but decreased accumulation of chlorophylls in the light. Two possible points of attack are indicated by the present results decreased activity of chlorophyll synthetase and diminished accumulation of chlorophyll proteins, e.g. LHCP. 

S. Granik, S. Sassa (1971). 5-Aminolevulinic acid synthetase and control of heme and chlorophyll synthesis. In H.J. Vogel (Ed.), Metabolic Regulation (pp. 77-141) McGraw-Hill, New York. 

In Pennisetum seedlings treated with difunon in higher concentration (>10 iM), the bleaching of pigments was reported to be paralleled by a decrease of the porphobilinogenase level whereas the contents of -aminolevulinic synthetase and dehydratase were not lowered ( 4). This proposed mode of action of difvinon upon chlorophyll biosynthesis could not be confirmed with the microalga Chlorella (23). 

It appears, then, that starch synthetase can exist in different forms, with rather different specificities tx)wards the possible glucosyl donors. The balance between these forms can be developmentally regulated and appears to differ with the tissue under study. Indeed, starch may be synthesised in a variety of organelles, varying from chloroplasts, though chlorophyll-free plastids and amyloplasts to large starch grains tenuously bounded by membrane. All are related, but are not identical. 

In animals the control of heme biosynthesis appears to be primarily a control on the rate of biosynthesis of the enzyme ALA-synthetase. Recent experiments [Sassa and Granick, 21] suggest that control of this enzyme occurs at both the transcription and the translation levels. Because these controls have been studied mainly in the liver, we shall discuss the evidence for the control mechanisms in this tissue, particularly the more recent work using chick embyro liver cells grown in primary culture. In later sections we shall discuss the ALA-synthetase control mechanism in the red cells for heme and hemoglobin synthesis, and the control mechanisms for chlorophyll synthesis in plants. 

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