J. Biol. Chem., Vol. 255, Issue 23, 11130-11134, 12, 1980
Role of heme in the synthesis of cytochrome c oxidase in Neurospora crassa
CC Kumar and G Padmanaban
The role of heme in the synthesis of cytochrome c oxidase has been
investigated in the mold Neurospora crassa. Iron-deficient cultures of the
mold have low levels of cytochrome oxidase and delta- aminolevulinate
dehydratase, the latter being the rate-limiting enzyme of the
heme-biosynthetic pathway in this organism. Addition of iron to the
iron-deficient cultures results in an immediate increase in the levels of
delta-aminolevulinate dehydratase followed by an increase in the rate of
heme synthesis and cytochrome oxidase levels. The rate of precursor
labeling of the mitochondrial subunits of cytochrome oxidase is decreased
preferentially under conditions of iron deficiency and addition of iron
corrects this picture. Exogenous hemin addition which prevents
iron-mediated induction of delta-aminolevulinate dehydratase also inhibits
the increase in the activity of cytochrome oxidase and the enhanced
precursor labeling of the mitochondrial subunits of cytochrome oxidase.
Protein synthesis on mitoribosomes measured in vivo and in vitro is
decreased under conditions of heme deficiency. Hemin addition in vitro to
mitochondrial lysates prepared from heme-deficient mycelia restores a near
normal rate of protein synthesis. It is concluded that heme is required for
the optimal rate of translation on mitoribosomes.
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