The metabolism of chlorophylls and related tetrapyrroles directly influences,
and is influenced by, the proteins and
cell structures with which they are associated. During net accumulation,
de-greening and at the steady state,
chlorophyll and its derivatives are important elements in the post-translational
regulation of the expression of
genes for chloroplast proteins. At the same time, they represent
potential photodynamic hazards against which
green cells need to have protective mechanisms. This review deals
with genetic, chemical and environmental
perturbations of chlorophyll biosynthesis that impact on protein stability,
membrane organization and
susceptibility to photodamage. NADPH-protochlorophyllide oxidoreductase is
considered in detail as a pigment-protein regulating, and regulated
by, chlorophyll metabolism. The question of the extent and significance of
chlorophyll turnover at the steady state is addressed, with particular
emphasis on the dynamics of the photosystem
II reaction centre. The pathway of chlorophyll catabolism is described,
along with its interrelationship with
protein mobilization in chloroplast senescence. Finally, the structural
basis of pigment–protein interaction and
stability is examined, and the discussion ends by expressing
some general thoughts about the control of protein
lifetimes in the living cell.