Supernatant protein factor facilitates intermembrane transfer of squalene.

نویسندگان

  • E J Friedlander
  • I W Caras
  • L F Lin
  • K Bloch
چکیده

Squalene epoxidation of microsome-associated squalene is stimulated by a soluble protein termed "supernatant protein factor" (SPF) (Saat, Y. A., and Bloch, K. E. (1976)J. Biol. Chem. 251, 5155-5160). In the absence of SPF, the initial rate for microsome-bound squalene epoxidation is rapid for 5 to 10 min but falls off sharply thereafter. SPF does not affect the rapid initial epoxidation rate of reaction but maintains it for longer periods. This SPF effect on enzyme kinetics indicates that SPF facilitates the otherwise rate-limiting access of squalene to the epoxidse site. Trypsin treatment of microsomes totally inactivates squalene epoxidase. When such trypsin-treated squalene-containing microsomes are incubated with normal, squalene-free, enzymatically active microsomes, formation of squalene epoxide is not observed. However, if SPF is included in this system, conversion of squalene to 2,3-oxidosqualene occurs rapidly. Lowering the temperature from 37 degrees to 22 degrees C abolishes the SPF effect in assay systems containing either normal or trypsin-treated plus normal microsomes. These findings show that SPF promotes the transfer of squalene from one microsome population to another, i.e. intermembrane transfer of substrate.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Supernatant protein factor, which stimulates the conversion of squalene to lanosterol, is a cytosolic squalene transfer protein and enhances cholesterol biosynthesis.

Squalene epoxidase, a membrane-associated enzyme that converts squalene to squalene 2,3-oxide, plays an important role in the maintenance of cholesterol homeostasis. In 1957, Bloch and colleagues identified a factor from rat liver cytosol termed "supernatant protein factor (SPF)," which promotes the squalene epoxidation catalyzed by rat liver microsomes with oxygen, NADPH, FAD, and phospholipid...

متن کامل

Squalene Epoxidase of Rat Liver*

The microsomal enzyme system from rat liver which catalyzes the epoxidation of squalene to 2,3-oxidosqualene (squalene epoxidase) has been investigated further with 10 ,ll-dihydrosqualene as the artacial substrate. Liver supernatant contributes two essential components to the epoxidase system, one heat stable and the other heat labile (YAMAMOTO, S., AND BLOCH, K. (1970) J. Biol. Chem. 245, 1670...

متن کامل

Liver Supernatant or Sterol Carrier Protein1 in the Enzymatic Conversion of Farnesyl Pyrophosphate to Squalene by Rat Liver Microsomes*

Earlier studies (Rilling, H. C. (1972) Biochem. Biophys. Res. Commun. 46, 470-475) suggested the possibility that a sterol carrier protein participated in the enzymatic conversion of farnesyl pyrophosphate to squalene by liver microsomal membranes. In the present article the possible requirement for soluble proteins in liver 105,000 x g supernatant (Slos) in the enzymatic conversion of farnesyl...

متن کامل

Stimulation by unsaturated fatty acid of uptake in rat liver microsomes squalene

Supernatant protein factor (SPF) and anionic phospholipids such as phosphatidylglycerol (PG) stimulate squalene epoxidase activity in rat liver microsomes by promoting ['Hlsqualene uptake as well as substrate translocation (Chin, J., and K. Bloch. 1984. J Biol. C h . 259: 11735-11738). This process is postulated to be membrane-mediated and not carriermediated. Here we show that treatment of PG ...

متن کامل

Mitochondrial protein import: Mia40 facilitates Tim22 translocation into the inner membrane of mitochondria

The mitochondrial intermembrane space assembly (MIA) pathway is generally considered to be dedicated to the redox-dependent import and biogenesis of proteins localized to the intermembrane space of mitochondria. The oxidoreductase Mia40 is a central component of the pathway responsible for the transfer of disulfide bonds to intermembrane space precursor proteins, causing their oxidative folding...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:
  • The Journal of biological chemistry

دوره 255 17  شماره 

صفحات  -

تاریخ انتشار 1980