KIKUCHI, K., TAMURA, S., SHINEHA, R. and TSUIKI, S.
Characterization of Protein Phosphatases Associated with the Particulate Fraction from Rat Liver. Tohoku J. Exp. Med., 1990,
160 (4), 287-300 - Protein phosphatases associated with the particulate fraction from rat liver were studied by chromatographing the fraction on a DEAE-cellulose column and assaying the eluate with phosphorylase
a and glycogen synthase D as substrates. Phosphorylase phosphatase activity emerged as two peaks, termed P-1 and P-2 in order of elution, both of which were inhibited by Mn
2+ and Mg
2+. P-1 and P-2 were
Mr=50, 000 and 32, 000 proteins, respectively, and when treated with trypsin, P-1 converted to a form indistinguishable from P-2, to which protein phosphatase inhibitor-2 was a potent inhibitor. Thus P-2 appears to be the catalytic subunit of type-1 protein phosphatase even though it has been degrated proteolytically as evidenced by its relatively low
Mr. The elution profile of glycogen synthase phosphatase activity was entirely different. The activity obtained with 5mM Mn
2+ resolved into three peaks, the second-migrating M-2 being the largest. M-2 is an
Mr=70, 000 protein; but an attempt to purify it has been unsuccessful giving a product of
Mr=40, 000 and closely similar to the type-1 catalytic subunit in properties including inhibition by inhibitor-2. These results suggest that phosphatases P-1 and M-2 have a common catalytic subunit (type-1), which is bound to different “regulatory” subunits. M-2 distributes in glycogen particles and microsomes evenly while P-1 is almost exclusively in microsomes.-protein phosphatase; glycogen synthase; phosphorylase phosphatase; rat liver; rat liver particulate fraction
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