Abstract
Abstract A cyclic AMP (adenosine 3', 5'-monophosphate)-dependent protein kinase has been found in membranes derived from human erythrocytes which accounts for greater than 70% of the total cyclic AMP-dependent protein kinase activity of these cells. Components of the erythrocyte membranes were phosphorylated by membrane-bound protein kinase, but stimulation of the rate of phosphorylation by cyclic AMP was observed only when histones or protamine served as substrates. The membrane-associated cyclic AMP-dependent protein kinase resembles many soluble protein kinases; it requires 20 mm Mg2+ for maximal activity, has apparent Km values of 26 µg per ml and 8.3 µm for protamine and ATP, respectively, and a Ka for cyclic AMP of 28 nm. Erythrocyte membranes specifically bind cyclic AMP and exhibit a dissociation constant of 3.3 nm for the membrane-cyclic AMP complex. Cyclic AMP-independent protein kinase activity was dissociated from the membrane by treatment with 1 m NH4Cl, but the cyclic AMP-binding activity was retained by the particulate fraction. These findings suggest that the cyclic AMP-binding moiety is firmly integrated into the membrane structure, whereas the catalytic moiety may only be loosely associated with the membrane.
Highlights
Cyclic AMP-independent protein kinase activity was dissociated from the membrane by treatment with 1 M
NH&l, but the cyclic AMP-binding activity was retained by the particulate fraction
These findings suggest that the cyclic AMP-binding moiety is firmly integrated into the membrane structure, whereas the catalytic moiety may only be loosely associated with the membrane
Summary
A cyclic AMP (adenosine 3’, 5’-monophosphate)-dependent protein kinase has been found in membranes derived from human erythrocytes which accounts for greater than 70% of the total cyclic AMP-dependent protein kinase activity of these cells. Components of the erythrocyte membranes were phosphorylated by membrane-bound protein kinase, but stimulation of the rate of phosphorylation by cyclic AMP was observed only when histones or protamine served as substrates. Rat brain synaptic membrane vesicles, and membrane fragments exhibited considerable cyclic AMP-dependent protein kinase activity when histone was used as substrate [15]. [16] reported that 50% of the cyclic AMP-dependent protein kinase activity in bovine anterior pituitary glands was associated with microsomal and nuclear fractions. The studies reported here are concerned with some of the properties of cyclic AMP-dependent protein kinase in membranes of human erythrocytes
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