Protein phosphatase composition in the smooth muscle of guinea-pig ileum studied with okadaic acid and inhibitor 2.
Using okadaic acid, a potent inhibitor of type 2A and type 1 protein phosphatases, and inhibitor 2, an intrinsic inhibitory factor of type 1 phosphatase, we characterized the phosphorylated myosin light-chain (PMLC) phosphatase activity in the smooth-muscle extracts of guinea-pig ileum. In the intact fibres the control activity was 254 +/- 13 nmol of Pi/min per g wet wt. (n = 15) against 32P-labelled PMLC (4 microM) from chicken gizzard. The following phosphatase fractions were identified: an inhibitor-2-sensitive (type 1) fraction (fractional activity = 35%), a Mg2+-dependent and okadaic acid-insensitive (type 2C) fraction (17%), and two type 2A-like fractions that had different susceptibility to okadaic acid. The type 2A-like fraction with lower affinity to okadaic acid accounted for 30% of the control activity. After the cell membrane was permeabilized by Triton X-100, more than 60% of this fraction remained and accounted for about 90% of the total activity, whereas the other fractions were nearly abolished. The type 2A-like fraction may be bound to some intracellular structure such as contractile proteins.
Takai
A
A
II. Physiologisches Institut, Universität Heidelberg, Federal Republic of Germany.
Troschka
M
M
Mieskes
G
G
Somlyo
A V
AV
D000818:Animals; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D006168:Guinea Pigs; D007082:Ileum / Q000201:enzymology; D007476:Ionophores; D008274:Magnesium / Q000502:physiology; D009124:Muscle Proteins; D009130:Muscle, Smooth / Q000201:enzymology*; D043263:Myosin-Light-Chain Phosphatase; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011506:Proteins; D000097847:Protein Phosphatase Inhibitory Proteins
D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D007476:Ionophores; D008274:Magnesium; D009124:Muscle Proteins; D043263:Myosin-Light-Chain Phosphatase; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D011506:Proteins; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins