Effect of proteolysis on the yeast mitochondrial deoxyribonucleases

Abstract

One or two forms of deoxyribonuclease may be found when yeast mitochondrial membranes are extracted by treatment with Triton X-100 at high ionic strength. The two forms can be separated by chromatography on DEAE-cellulose. The forms differ from one another by their physical and catalytic properties: form I, retained on the column, degrades double-stranded and single-stranded DNA at neutral pH, and is not stimulated by ethidium bromide; form II (or ethidium bromide-activated DNAase), not retained on the column. degrades ss-DNA at neutral pH, and ds-DNA at pH 5.8. Form II is about 30-fold stimulated by ethidium bromide at pH 7.8. Most probably, form II derived from form I through a limited proteolytic process. This conversion depends on such factors as the storage of the mitochondrial extract or the physiological state of the cells. Form II is found when cells are harvested at stionary phase, coincident with the increment of the yeast proteinases; its formation is blocked by the ddition of proteinase inhibitors to the extract. Conversion of form I to form II, which is associated with a change in the sedimentation coefficient of the enzumatic proteins from 5.4 S to 4.5 s, can be reproduced in vitro by treatment with α-chymotrypsin.