Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.26.9 (ribonuclease)
 6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A variety of proteins have been studied for their ability to interact and alter the thermotropic properties of phospholipid bilayer membranes as detected by differential scanning calorimeter. The proteins studied included: basic myelin protein (A1 protein), cytochrome c, major apoprotein of myelin proteolipid (N-2 apoprotein), gramicidin A, polylysine, ribonuclease and hemoglobin. The lipids used for the interactions were dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol. The interactions were grouped in three catagories each having very different effects on the phospholipid phase transition from solid to liquid crystalline. The calorimetric studies were also correlated with data from vesicle permeability and monolayer expansion. Ribonuclease and polylysine which exemplify group 1 interactions, show strong dependence on electrostatic binding. Their effects on lipid bilayers include an increase in the enthalpy of transition (deltaH) accompanied by either an increase or no change in the temperature of transition (Tc). In addition, they show minimal effects on vesicle permeability and monolayer expansion. It was concluded that these interactions represent simple surface binding of the protein on the lipid bilayer without penetration into the hydrocarbon region. Cytochrome c and A1 protein, which exemplify group 2 interactions, also show a strong dependence on the presence of net negative charges on the lipid bilayers for their binding. In contrast to the first group, however, they induce a drastic decrease in both Tc and deltaH of the lipid phase transition. Furthermore, they induce a large increase in the permeability of vesicles and a substantial expansion in area of closely packed monolayers at the air-water interface. It was concluded that group 2 interactions represent surface binding followed by partial penetration and/or deformation of the bilayer. Group 3 interactions, shown by proteolipid apoprotein and gramicidin A, were primarily non-polar in character, not requiring electrostatic charges and not inhibited by salt and pH changes. They had no appreciable effect on the Tc but did induce a linear decrease in the magnitude of the deltaH, proportional to the percentage of protein by weight. Membranes containing 50% proteolipid protein still exhibited a thermotropic transition with a deltaH one half that of the pure lipid, and only a small diminution of the size of the cooperative unit. It was concluded that in this case the protein was embedded within the bilayer, associating with a limited number of molecules via non-polar interactions, while the rest of the bilayer was largely unperturbed.
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PMID:Effects of proteins on thermotropic phase transitions of phospholipid membranes. 5 74

Cytochrome c, a "mobile electron carrier" of the mitochondrial respiratory chain, also occurs in detectable amounts in the cytosol, and can receive electrons from cytochromes present in endoplasmic reticulum and plasma membranes as well as from superoxide and ascorbate. The pigment was found to dissociate from mitochondrial membranes in liver and kidney when rats were subjected to heat exposure and starvation, respectively. Treating cytochrome c with hydroxylamine gives a partially deaminated product with altered redox properties; decreased stimulation of respiration by deficient mitochondria, increased reduction by superoxide, and complete loss of reducibility by plasma membranes. Mitochondria isolated from brown adipose tissue of cold-exposed rats are found to be sub-saturated with cytochrome c. The ability of cytochrome c to reactivate reduced ribonuclease is now reinterpreted as a molecular chaperone role for the hemoprotein.
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PMID:Functions of cytochrome c in regulation of electron transfer and protein folding. 132 35

A method for studying inhibitors of the contact stages of blood coagulation is described. A number of positively charged substances were shown to inhibit the contact stages. The inhibitory substances include spermine, cytochrome c, ribonuclease, and lysozyme. The inhibitory effect of these substances was neutralized by the addition of an activated plasma thromboplastin antecedent, factor XI, (PTA) fraction. Other positively charged substances including protamine, hexadimethrine, polylysine, polyornithine, methylene blue, and ortho-toluidine blue also inhibited the contact stages of coagulation, but the inhibitory effect on coagulation was not neutralized by the activated PTA fraction. Negatively charged substances such as heparin and insulin did not inhibit the contact stages of coagulation. Cytochrome c inhibited Celite adsorption of a partially purified Hageman factor fraction, and cytochrome, ribonuclease, spermine, and lysozome inhibited the adsorption of Hageman factor from PTA-deficient plasma. Very much smaller quantities of Celite completely adsorbed Hageman factor from the fraction rather than from whole plasma, which suggested the possibility that plasma contains an inhibitor or inhibitors of Hageman factor adsorption. Furthermore cytochrome c, spermine, ribonuclease, and lysozyme inhibited the coagulant activity of the following activators of the Hageman and PTA factors: Celite, kaolin, sodium stearate, ellagic acid, and skin. It is suggested that negatively charged sites on these activators are critical for adsorption and activation and that inhibition results from neutralization of the negatively charged sites by the adsorbed inhibtor. Tests with polylysine polymers indicate that inhibitory activity is directly related to molecular size over the molecular weight range of 4000 to 100,000.
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PMID:Inhibition of Hageman factor activation. 564 60