Role of SH groups in the activity of pig phosphorylase b isoenzymes.

The reaction of phosphorylases from rabbit skeletal muscle, pig skeletal muscle and pig heart with DTNB and the effects of AMP and glucose-6-phosphate on the above reaction were examined and compared. The SH groups of pig heart-specific phosphorylase b were found to be the same as those of rabbit skeletal muscle. Pig skeletal muscle phosphorylase b differed from the foregoing enzymes in that its slowly reacting SH groups played a minor role in the catalytic activity and AMP and glucose-6-phosphate affected neither the DTNB reaction nor the small decrease of activity during the reaction.