MECHANISMS OF REGULATION AND INTERPLASTID LOCATION OF CHLOROPHYLL BIOSYNTHESIS

The current concepts of chlorophyll biosynthesis, its interplastid loc ation, biosynthetic and biochemical heterogeneity, mechanisms of regul ation of the key reactions - 5-aminolevulinic acid formation and magne sium incorporation into protoporphyrin IX - are reviewed. The literatu re and own data of the author demonstrate the existence in plants of s pecific multienzymatic systems synthesizing chlorophyll and its precur sors as monovinyl and divinyl chemical species. Both type of multienzy matic systems synthesize 5-aminolevulinic acid and regulate this proce sses independently. The hypothesis is considered that a mechanism exis ts that controls the function of the magnesium branch of chlorophyll b iosynthesis in vivo through inhibition of the enzymes by their product s because of limitation of binding sites for them in the membrane. An additional influence of light on the Mg-chelatase activity not only vi a the photosynthetic supply with ATP but also through the light-induce d synthesis of the enzyme molecules de novo is described. The efficien t energy migration from protoporphyrin IX and Mg-protoporphyrin IX (mo nomethyl ester) molecules to the photochlorophyllide active form detec ted by the author is discussed considering a close location of these p igments in plastid membranes as well as the enzymes participating in t heir formation.