Separation of fractions of phosphoprotein phosphatase and its protein inhibitors by isoelectrofocusing

• Published in: Biokhimiia (Moscow, Russia) Vol. 46; no. 7; p. 1236
• Main Authors: Parsadanian, G K, Ter-Tatevosian, L P, Sherstnev, K B
• Format: Journal Article
• Language: Russian
• Published: Russia (Federation) 01-07-1981
• Subjects: Animals; Isoelectric Focusing; Myocardium - enzymology; Phosphoprotein Phosphatases - antagonists & inhibitors; Phosphoprotein Phosphatases - isolation & purification; Proteins - isolation & purification; Proteins - physiology; Rats
• ISSN: 0320-9725

Individual molecular forms of phosphoprotein phosphatase from albino rat cardiac muscle were separated by isoelectrofocusing, resulting in a few fractions differing in pI (5.1, 5.4, 5.9-6.1 (double peak) and 7.1, respectively). Isoelectrofocusing of a purified enzyme preparation also allowed to isolate and characterize two protein inhibitors of the enzyme. The first one with pH 6.5-6.7 is similar to the thermostable phosphoprotein phosphatase inhibitor known from literature. This protein inhibits the enzyme activity by 90%; its effect is not decreased after 5-min heating at 95 degrees. The other inhibitor protein with pH 5.6-5.8 is thermolabile. When the enzyme activity was decreased 2.5-fold prior to thermal treatment, the latter protein lost this ability after heating at 95 degrees and inhibited the enzyme only by 9%. It is assumed that inhibitory proteins beside low molecular weight effectors can be involved in the mechanisms of the post-synthetical operative modification of phosphoprotein phosphatase function.