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R L Jilka

Publications and source records attributed to R L Jilka.

63 records · Page 4Linked to original sources
PubMed1979

Ornithine transcarbamylase of rat liver. Kinetic, physical, and chemical properties.

Ornithine transcarbamylase of rat liver has been purified to homogeneity. The purified enzyme of specific activity 870 to 920 focuses as a single protein at pH 7.2. At pH 7.7, the Km for carbamyl phosphate is 0.026 mM, and the Km for ornithine is 0.04 mM. The inhibition constants of a number of amino acids that act as competitive inhibitors of the enzyme are reported. The native enzyme of Mr = 112,000 is composed of three subunits of Mr = 39,600 +/- 1,000. Chemical evidence indicates that the subunits are identical in amino acid composition and amino acid sequence. The amino acid sequence of the NH2-terminal region of ornithine transcarbamylase is Ser-Gln-Val-Gln-Leu-Lys-Gly-Ser-Asp-Leu-Leu-Thr-Leu-Lys-Asn-(Phe)-X-Thr-X-Glu-Ile-Gln-Tyr-Met-.

Amino Acid Sequence↗
PubMed1979

Precursor sequence of MOPC-315 mouse immunoglobulin heavy and light chains.

Partially purified mRNA coding for the MOPC-315 heavy (alpha) or light (lambda 2) immunoglobulin chain was translated in a nuclease-treated reticulocyte lysate containing 20 labeled amino acids. Radiolabeled precursor heavy and light chains, purified by immunoprecipitation and preparative gel electrophoresis, were subjected to Edman degradation. The labeled phenylthiohydantoin derivatives obtained in each degradative cycle were identified and quantitated by high pressure liquid chromatography. Both heavy and light chain precursor segments were hydrophobic in nature; however, they were not homolgous in sequence. To establish whether COOH-terminal proteolytic processing of the heavy chain might also be occurring during secretion, the cyanogen bromide peptides of the heavy chain precursor were compared to those of the mature secreted heavy chain. The results indicated that the COOH termini of the two chains were identical.

Amino Acid Sequence↗
PubMed1977

The effect of calcium ion transport ATPase upon the passive calcium ion permeability of phospholipid vesicles.

The uptake and release of Ca2+ by sarcoplasmic reticulum fragments and reconstituted ATPase vesicles was measured by a stopped-flow fluorescence method using chlortetracycline as Ca2+ indicator. Incorporation of the Ca2+ transport ATPase into phospholipid bilayers of widely different fatty acid composition increases their passive permeability to Ca2+ by several orders of magnitude. Therefore in addition to participating in active Ca2+ transport, the (Mg2+ + Ca2+)-activated ATPase also forms hydrophilic channels across the membrane. The relative insensitivity of the permeability effect of ATPase to changes in the fatty acid composition of the membrane is in accord with the suggestion that the Ca2+ channels arise by protein-protein interaction between four ATPase molecules. The reversible formation of these channels may have physiological significance in the rapid Ca2+ release from the sarcoplasmic reticulum during activation of muscle.

Adenosine Triphosphatases↗
PubMed1977

Amino acid sequence of the precursor region of MOPC-315 mouse immunoglobulin heavy chain.

Partially purified mRNA coding for the MOPC-315 heavy immunoglobulin alpha chain was translated in a reticulocyte lysate containing 20 labeled amino acids. Radiolabeled MOPC-315 heavy chain precursor protein, purified by preparative gel electrophoresis and immunoprecipitation, was sequenced by Edman degradation. The labeled phenylthiohydantoin amino acid obtained in each cycle was identified and quantitated by high-pressure liquid chromatography. The precursor sequence of 18 amino acids, Met-Lys-Val-Leu-Ser-Leu-Leu-Tyr-Leu-Leu-Thr-Ala-Ile-Pro-His-Ile-Met-Ser, preceded the sequence corresponding to the NH2 terminus of the mature secreted heavy chain.

Amino Acid Sequence↗
PubMed1976

Mechanism of ATP hydrolysis by sarcoplasmic reticulum and the role of phospholipids.

Exchange of sarcoplasmic reticulum phospholipids with dipalmitoyllecithin inhibits the (Mg2+ + Ca2+)-activated ATPase activity below 40 degrees by inhibition of the decomposition of phosphoprotein intermediate. The rate of phosphoprotein formation and the steady state concentration of phosphoprotein measured by rapid kinetic techniques are affected to a lesser extent. The inhibitory effect of dipalmitoyllecithin on ATPase activity is probably related to the viscosity of the hydrocarbon region of the membrane which inhibits the conformational change leading to calcium translocation and the eventual cleavage of phosphoprotein.

Adenosine Triphosphatases↗
PubMed1975

Passive Ca2+ permeability of phospholipid vesicles and sarcoplasmic reticulum membranes.

During the excitation of muscle the estimated rate of Ca2+ release from sarcoplasmic reticulum may increase 10(3)- to 10(4)-fold compared with relaxed muscle or isolated sarcoplasmic reticulum in vitro, implying a major change in the calcium permeability of the sarcoplasmic reticulum membrane. As a first step in the assessment of the role of various membrane constituents in the regulation of calcium fluxes, the contribution of phospholipids to the definition of calcium permeability was studied in model systems. The rate of calcium release from vesicles prepared from pure phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositides, cardiolipin, and extracted microsomal lipids is in the range of 10(-15) to 10(18) mol of calcium/cm2/s. This rate is several orders of magnitude lower than the passive calcium outflux from isolated sarcoplasmic reticulum membranes. The permeability to Ca2+ is influenced by fatty acid composition and net charge and it is markedly increased with increasing temperature or after the addition of local anesthetics.

Anesthetics, Local↗
PubMed1975

Effect of the purified (Mg2+ + Ca2+)-activated ATPase of sarcoplasmic reticulum upon the passive Ca2+ permeability and ultrastructure of phospholipid vesicles.

The passive Ca2+ permeability of fragmented sarcoplasmic reticulum membranes is 10(4) to 10(61 times greater than that of liposomes prepared from natural or synthetic phospholipids. The contribution of membrane proteins to the Ca2+ permeability was studied by incorporating the purified [Ca2+ + Mg2+]-activated ATPase into bilayer membranes prepared from different phospholipids. The incorporation of the Ca2+ transport ATPase into the lipid phase increased its Ca2+ permeability to levels approaching that of sarcoplasmic reticulum membranes. The permeability change may arise from a reordering of the structure of the lipid phase in the environment of the protein or could represent a specific property of the protein itself. The calcium-binding protein of sarcoplasmic reticulum did not produce a similar effect. The increased rate of Ca2+ release from reconstituted ATPase vesicles is not a carrier-mediated process as indicated by the linear dependence of the Ca2+ efflux upon the gradient of Ca2+ concentration and by the absence of competition and countertransport between Ca2+ and other divalent metal ions. The increased Ca2+ permeability upon incorporation of the transport ATPase into the lipid phase is accompanied by similar increase in the permeability of the vesicles for sucrose, Na+, choline, and SO42- indicating that the transport ATPase does not act as a specific Ca2+ channel. Native sarcoplasmic reticulum membranes are asymmetric structures and the 75-A particles seen by freeze-etch electron microscopy are located primarily in the outer fracture face. In reconstituted ATPase vesicles the distribution of the particles between the two fracture faces is even, indicating that complete structural reconstitution was not achieved. The Ca2+ transport activity of reconstituted ATPase vesicles is also much less than that of fragmented sarcoplasmic reticulum. The density of the 40-A surface particles visible after negative staining of native or reconstituted vesicles is greater than that of the intramembranous particles and the relationship between these two structures remains to be established.

Adenosine Triphosphatases↗