Envelope and thylakoid membranes from pea (Pisum sativum var. Laxton's Progress No. 9) chloroplasts were analyzed for the presence of glycoproteins using two different approaches. First, the sugar composition of delipidated membrane polypeptides was measured directly using gas chromatographic analysis. The virtual absence of sugars suggests that plastid membranes lack glycoproteins. Second, mem...

Stearoyl-coenzyme A desaturase (SCD) is a key regulator of membrane fluidity, turns over rapidly, and represents a prototype for selective degradation of resident proteins of the endoplasmic reticulum. Using detergent-solubilized, desaturase-induced rat liver microsomes we have characterized a protease that degrades SCD. Degradation of SCD in vitro is highly selective, has a half-life of 3-4 h,...

The microsomal fraction from the mesocarp of avocado (Persea americana) is one of few identified rich sources of plant cytochrome P-450. Cytochrome P-450 from this tissue has been solubilized and purified. Enzymatic assays (p-chloro-N-methylaniline demethylase) and spectroscopic observations of substrate binding suggest a low spin form of the cytochrome, resembling that in the microsomal membra...

Two widely used antipsychotic drugs, chlorpromazine (CPZ) and trifluoperazine (TFZ) inhibit NADPH-induced microsomal lipid peroxidation (LPO). Study of microsomal membrane fluidity revealed considerable disorganization in its architecture in the presence of NADPH, which can be restored back in the presence of CPZ and TFZ. NADPH-dependent microsomal LPO is catalyzed by NADPH: cytochrome P450 red...

Purified rough microsomes from liver maximally incorporated N-acetyl-[3H]glucosamine into endogenous acceptors from UDP-N-acetyl-[3H]glucosamine substrate, providing the associated ribosomes were removed and 0.5 mM GTP was added. These conditions also led to the coalescence of microsomes into large fused membranes. By measurement of membrane profiles on electron micrographs, a correlation was o...

A bulk fraction enriched with respect to neuronal cell bodies was used as starting material for the isolation of neuronal plasma membrane The cells were gently homogenized in isotonic sucrose and a crude membrane containing fraction sedimented at 3000 g. Subsequently, the membrane fraction was purified on a discontinuous sucrose density gradient between 35% and 25 5% sucrose (w/w). Enzymatic an...

The sodium dodecyl sulfate (SDS)-solubilized proteins of the bileaflet nuclear membrane from rat liver have been fractionated by gel Htration. More than 23 different molecular weight classes of proteins ranging from 160,000 to 16,000 can be distinguished by conventional SDS-polyacrylamide gel electrophoresis. Polypeptide chains of less than 16,000 were not detected. A triplet, the respective pr...

We investigated the transmembrane topology of the GluR3 subunit that was translated in rabbit reticulocytes supplemented with microsomal membranes. A prolactin reporter epitope was fused to GluR3 at six locations, bracketing each of the proposed transmembrane domains. The sidedness of the epitope in the microsomal membrane was then assessed by proteinase K sensitivity. The N terminus and the en...

The transport of FAD and its effect on disulfide bond formation was investigated in rat liver microsomal vesicles. By measuring the intravesicular FAD-accessible space, we observed that FAD permeates across the microsomal membrane and accumulates in the lumen. Rapid filtration experiments also demonstrated the uptake and efflux of the compound, which could be inhibited by atractyloside and 4,4'...

A number of Saccharomyces cerevisiae membrane-bound oxidoreductases were examined for potential roles in microsomal fatty acid elongation, by assaying heterologous elongating activities in individual deletion mutants. One yeast gene, YBR159w, was identified as being required for activity of both the Caenorhabditis elegans elongase PEA1 (F56H11.4) and the Arabidopsis thaliana elongase FAE1. Ybr1...