Inhibition of phosphorylase phosphatase by polyamines

Phosphorylase phosphatase from rabbit liver or from bovine heart, purified as the M r 35,000 form, is inhibited by the naturally occurring polyamines, spermine and spermidine. The inhibition is apparently competitive with a K i of 0.037 mM for spermine and 0.65 mM for spermidine. Further investigation showed that the inhibition is substrate-directed, i.e. due to an interaction of the polyamines with the rabbit muscle phosphorylase a used as the substrate.