Changes of glycogen phosphorylase isozyme pattern, in rat tissues during pre- and postnatal development.

: Quantitative estimates of M- and L-type phosphorylase subunits in adult and developing rat tissues have been obtained by immunotitration of tissue extracts with subunit-specific antibodies. It has been shown that M-type subunits occur in all studied tissues with exception of adult liver and placenta. L-type subunits account for most of the total phosphorylase activity in liver and bone marrow but are present also in a variety of other adult and in most of the fetal tissues examined. During maturation, selective increases in the expression of phosphorylase isozymes occur in certain tissues such as liver, brain, heart and skeletal muscle. The hitherto unknown hybrid LM has been produced by in vitro hybridization of M- and L-subunits.