THE PROTEINS OF THE DILUTION PRECIPITATE OBTAINED FROM SALT EXTRACTS OF PREGNANT AND NON-PREGNANT UTERUS

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Abstract
The presence of actomyosin in dilution precipitates made from extracts of uterus muscle (extracted with buffered 0.5 [image]-potassium chloride -1.5 [image]- ATP, and diluted to 0.04 [image]) was confirmed; little or no free myosin was found. With pregnant-rabbit uteri near term, about 45% of this protein precipitate was actomyosin; with uteri of non-pregnant rabbits or pigs, the amount was only about 25%. The actomyosin content of myometrium is thus less than 10% of that in skeletal muscle. On fractionation with ammonium sulphate, especially with non-pregnant uteri, much of the protein (up to 35%) was precipitated at 16-26% saturation. This precipitate contained some actomyosin or myosin and some salt-soluble collagen, but no free actin. The soluble proteins associated with the actomyosin in the dilution precipitate were studied. These cannot be separated by repeated precipitation by dilution to 0.04 [image], but can be isolated by dilution in stages. The soluble proteins of the T fraction, prepared as described by Ivanov et al., have also been investigated. This contained material of high electrophoretic mobility (probably tropomyosin B). The soluble protein from both sources gave solutions of low viscosity; in both cases viscosity measurements suggest the presence of 10-15% of tropomyosin B. The nucleic acid content of the dilution precipitates and of the various fractions made from them was estimated. The effect of removal of nucleic acid on the behavior of the proteins was investigated.