Cell nuclear DNases: multiplicity and heterogeneity
Basnak'ian, A.G.; Bubnov, N.V.; Votrin, I.I.
Biokhimiia 54(2): 273-283
1989
ISSN/ISBN: 0320-9725 PMID: 2545281 Document Number: 326731
In order to determine the ratio of activities of major endonucleases of rat liver chromatin, a stepwise fractionation of cell nuclear extracts by chromatography on phosphocellulose and gel filtration through Toyopearl HW60 was carried out. This procedure resulted in partially purified preparations of Ca2+, Mg2+-dependent endonuclease (55 .+-. 10 kD), Ca2+, Mg2+-dependent endonuclease (30 .+-. 10 kD), Mn2+-dependent endonuclease (30 .+-. .+-. 5 kD) and acid cation-independent endonuclease. The Ca2+, Mg2+-dependent endonuclease with Mr of 55 .+-. 10 kD made up by 57% of the nuclear extract activity in the presence of Ca2+ + Mg2+ and revealed a high calcium-magnesium synergism. Under the same experimental conditions, the 30 .+-. 10 kD enzyme made up to 33% of the nuclear extract activity and revealed a low synergism. The activity of Mn2+-dependent endonuclease made up to 26% of the total nuclear extract activity in the presence of Mn2+, that of acid endonuclease-11% of the extract activity in 1 mM EDTA at pH 5.0. It was assumed that the low molecular weight Ca2+, Mg2+-dependent endonuclease represents a product of limited proteolysis of high molecular weight Ca2+, Mg2+-dependent endonuclease.