S. Kirkeby et al., BIOTIN CARBOXYLASES IN MITOCHONDRIA AND THE CYTOSOL FROM SKELETAL ANDCARDIAC-MUSCLE AS DETECTED BY AVIDIN BINDING, Histochemistry, 100(6), 1993, pp. 415-421
Biotin carboxylases in mammalian cells are regulatory enzymes in lipog
enesis and gluconeogenesis. In this study, endogenous biotin in skelet
al and cardiac muscle was detected using avidin conjugated with alkali
ne phosphatase and applied in high concentrations to muscle sections.
The avidin binding was subsequently visualized by histochemical demons
tration of the alkaline phosphatase activity. All cardiac muscle cells
showed high affinity for avidin with only the nuclei and the intercal
ated discs remaining unstained. In skeletal muscle a diffuse reaction
could be detected in the sarcoplasm of the muscle fibres. A granular r
eaction was noted in the same fibres that showed activity for succinic
dehydrogenase. The specificity of the coloured reaction product in th
e muscle sections was investigated and is suggested to be caused by av
idin binding to biotin moieties in mitochondria and the cytosol. Mitoc
hondrial and cytosolic preparations of skeletal muscle were electropho
resed in sodium dodecyl sulphate gels. After blotting and incubation w
ith conjugated avidin, two bands with molecular weights of 75 kDa and
130 kDa respectively were evident in the mitochondrial preparation. It
is suggested that the 75-kDa band represents comigration of the bioti
n-containing subunits of propionyl-CoA carboxylase and methylcrotonyl-
CoA carboxylase. The 130-kDa band may represent the biotin-containing
pyruvate carboxylase. In the cytosolic preparation a 270-kDa band was
stained in blots that had been incubated with conjugated avidin; this
band is suggested to represent acetyl-CoA carboxylase. A 190-kDa cytos
olic band might be a cleavage product of acetyl-CoA carboxylase. We pr
opose that using alkaline phosphatase-conjugated avidin it is possible
to detect the mitochondrial and cytosolic biotin-dependent carboxylas
es in striated muscle.