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P Strittmatter

Publications and source records attributed to P Strittmatter.

At least 55 records · Page 3Linked to original sources
PubMed1977

Cytochrome b5 and cytochrome b5 reductase-phospholipid vesicles. Intervesicle protein transfer and oreintation factors in protein-protein interactions.

NADH-cytochrome b5 reductase readily binds to preformed phospholipid vesicles either below or above the phase transition temperature of the lipid and in the absence of detergents. The isolated vesicles are free of unbound reductase, and the lipid is present as small, closed bilayers (250 to 400 A in diameter) as indicated by gel filtration, density gradient centrifugation, and internal volume measurements with [3H]glucose. The order of substrate specificity of the bound reductase is: ferricyanide = cytochrome b5 bound to reductase vesicles (100%) greater than cytochrome b5 heme peptide (13%) greater than unbound cytochrome b5 (4.5%) greater than cytochrome b5 vesicles (0.1%). This indicates that a specific orientation of cytochrome b5 and reductase in the bilayer is required for optimal interaction. Protein transfer occurs between reductase vesicles and cytochrome b5 vesicles. The transfer is time-dependent (40 to 70% complete in 2 h), does not involve vesicle fusion, is most rapid at the phase transition temperature of the phospholipid, and appears to require a fluid bilayer.

Animals↗
PubMed1976

Mechanism of rat liver microsomal stearyl-CoA desaturase. Studies of the substrate specificity, enzyme-substrate interactions, and the function of lipid.

The three purified proteins which are required for microsomal stearyl-CoA desaturation, NADH-cytochrome b5 reductase, cytochrome b5, and desaturase, have been combined with egg lecithin or dimyristyl lecithin vesicles to reconstruct a functional electron transport system capable of utilizing NADH and O2 in the desaturation of stearyl-CoA. Such preparations appear to consist of phospholipid vesicles which contain the three proteins bound to the outer surface of the vesicles. Acyl-CoA derivatives containing 12 to 19 carbon fatty acyl chains are required for desaturase activity while derivatives containing 9 to 20 carbons are capable of binding to the enzyme. Shorter chain acyl-CoA derivatives, free CoA, and free fatty acids do not appear to bind to the enzyme. Inhibition and analog studies suggest that the methylene chain of stearyl-CoA assumes an eclipsed ("gauche") conformation at carbon atoms 9,10 in the enzyme-substrate complex. Furthermore, isotope rate effects obtained with deuterated stearyl-CoA derivatives indicate that hydrogen removal is the rate-limiting step of desaturation. Stearyl-CoA binds to pure liposomes and desaturase-containing liposomes, and it is this form of stearyl-CoA which appears to be the substrate for desaturase. The Arrhenius plots of desaturase activity obtained using desaturase bound to egg lecithin liposomes, in which the liquid crystalline to crystalline phase transition temperature is -5 degrees, was linear between 15 and 35 degrees, while that obtained using desaturase bound to dimyristyl lecithin liposomes showed a break at 24 degrees coinciding with the liquid crystalline to crystalline phase transition temperature for this lipid. The decrease observed in the deuterium isotope rate effect below the transition temperature indicates that a step in the reaction sequence other than hydrogen abstraction becomes rate-limiting when the lipid is in the crystalline state. In this system translational diffusion does not emerge as the rate-limiting step. The liposomes contained sufficient reductase and cytochrome b5 so that translational diffusion was not rate-limiting.

Animals↗
PubMed1975

The interaction of NADH-cytochrome b5 reductase and cytochrome b5 bound to egg lecithin liposomes.

Incubation of liposomes prepared by sonication of egg lecithin with the amphipathic form of cytochrome b5 results in the binding of a maximum of 244 molecules of cytochrome b5 per liposomal vesicle. Interactions of the phospholipid with the hydrophobic segment of cytochrome b5 are involved in this binding which does not disrupt the liposome. When a small amount of NADH-cytochrome b5 reductase is bound liposomes simultaneously with cytochrome b5, the two proteins catalyze the reduction of cytochrome c by NADH. A qualitative kinetic analysis reveals that all of the cytochrome b5 interacts with reductase, a result consistent with these protein undergoing translational diffusion in the plane of the membrane. This system and the purified stearyl coenzyme A desaturase provide a model to study the dynamics of protein andlipid interactions in this membrane-bound oxidative sequence.

Animals↗
PubMed1975

Apparent dependence of interactions between cytochrome b5 and cytochrome b5 reductase upon translational diffusion in dimyristoyl lecithin liposomes.

Dimyristoyl lecithin liposomes, containing cytochrome b5 reductase (NADH:ferricytochrome b5 oxidoreductase, EC 1.6.2.2) and varying amounts of cytochrome b5, were used to measure flavoprotein catalysis alone and catalysis requiring electron transfer between the reductase and cytochrome as a function of temperature. Whereas flavoprotein catalysis showed a simple linear temperature dependence in an Arrhenius plot, the reaction involving electron transfer between the two bound enzymes showed a marked, 4-fold, change in rate at the crystalline-liquid crystalline phase transition of the hydrocarbon chains of the lecithin vesicles and a second, minor change involving the minor transition. These data represent strong evidence that protein-protein interactions in this membrane model system are dependent upon translational diffusion of nonpolar segments of the proteins in the hydrocarbon region of the phospholipid bilayer.

Animals↗
PubMed1974

Purification and properties of rat liver microsomal stearyl coenzyme A desaturase.

The terminal enzyme of the NADH-dependent stearyl coenzyme A desaturase system has been isolated from rat liver microsomes. This desaturase is a single polypeptide of 53,000 daltons containing 62% nonpolar amino-acid residues and one atom of non-heme iron. The purified protein forms high molecular weight aggregates that can be dispersed by detergent procedures. Desaturase activity requires NADH, stearyl coenzyme A, oxygen, lipid, and the three enzymes, cytochorme b(5) reductase (EC 1.6.2.2), cytochrome b(5), and desaturase. Cytochrome b(5) is the direct electron donor to the desaturase, which appears to utilize the iron in the oxidation-reduction sequence during desaturation of stearyl coenzyme A.

Animals↗
PubMed1971

A form of cytochrome b5 that contains an additional hydrophobic sequence of 40 amino acid residues.

A species of cytochrome b(5) with a monomer molecular weight of 16,700 has been isolated from rabbit-liver microsomes by a procedure that uses detergents and avoids the use of any proteolytic or lipolytic enzymes. This detergent-extracted cytochrome b(5) is larger than the trypsin- or lipase-extracted enzyme, and appears to contain an extremely hydrophobic appendage of 40 amino acids, probably at the N-terminus. The hydrophobic character of the extra amino acid sequence leads to aggregation in the absence of detergents, and may be of considerable importance in the binding of the enzyme to microsomes. It is suggested that the hydrophilic portion of the cytochrome molecule, which bears the heme and is enzymatically functional, is oriented toward the surface of the membrane where it readily reacts with nonmicrosomal proteins, while the hydrophobic "tail" anchors the heme protein tightly to the membrane.

Amino Acid Sequence↗