AJP - Cell Physiology, Vol 259, Issue 2 C310-C314, Copyright © 1990 by American Physiological Society
Regulation of 5'-aminolevulinate synthase activity in overloaded skeletal muscle
D. A. Essig, J. M. Kennedy and L. A. McNabney
Department of Physical Education, University of Illinois, Chicago 60680.
The regulation of the mitochondrial enzyme 5'-aminolevulinate synthase (ALV
synthase) activity during chronic weight-bearing activity (overload) in
chicken skeletal muscle was investigated. Maximal enzyme activity was
increased 2.5- and 4.0-fold after 3 and 7 days of overload. The content of
ALV synthase mRNA (ng/mg total RNA) was not changed after 3 days but
increased (20%; P less than 0.05) after 7 days of overload. Normalizing the
content of ALV synthase mRNA relative to the increase in total RNA
indicated that ALV synthase mRNA increased by 1.6- and 2.0-fold at 3 and 7
days, respectively. On this basis, the increase in enzyme activity per gram
protein exceeded the increase in mRNA content per gram protein by 60-70%.
During overload, the activity of cytochrome oxidase was unchanged after 3
days but increased by 1.5-fold (P less than 0.05) after 7 days of overload.
The data indicate that 1) the initial rise in ALV synthase mRNA and
activity due to overload occurs in the absence of a prior change in the
level of cytochrome oxidase, an enzyme that requires heme for its assembly,
and 2) induction of ALV synthase activity is regulated largely by processes
at the translational or posttranslational steps.
