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protein (pro´ten, pro´te-in)

Macromolecules consisting of long sequences of a-amino acids [H2N-CHR-COOH] in peptide (amide) linkage (elimination of H2O between the a-NH2 and a-COOH of successive residues). P. is three-fourths of the dry weight of most cell matter and is involved in structures, hormones, enzymes, muscle contraction, immunological response, and essential life functions. The amino acids involved are generally the 20 a-amino acids (glycine, l-alanine, etc.) recognized by the genetic code. Cross-links yielding globular forms of p. are often effected through the -SH groups of two sulfur-containing l-cysteinyl residues, as well as by noncovalent forces (hydrogen bonds, lipophilic attractions, etc.). [G. protos, first, + -in]
p. 4.1 a peripheral p. that binds tightly to spectrin in the red cell membrane; it also binds to certain glycophorins and helps determine the shape and flexibility of the red blood cell.
acute phase p. plasma p.'s including C-reactive p. (CRP), mannose-binding p., serum amyloid P component, a1-antitrypsin, fibrinogen, ceruloplasmin, and complement components C9 and factor B, the concentrations of which increase in response to interleukins 1, 6, and 11.
acyl carrier p. (ACP) one of the p.'s of the complex in cytoplasm that contains all of the enzymes required to convert acetyl-CoA (and, in certain cases, butyryl-CoA or propionyl-CoA) and malonyl-CoA to palmitic acid. This complex is tightly bound together in mammalian tissues and in yeast, but that from Escherichia coli is readily dissociated. The ACP thus isolated is a heat-stable p. with a molecular weight of about 10,000. It contains a free -SH that binds the acyl intermediates in the synthesis of fatty acids as thioesters. This -SH group is part of a 4´-phosphopantetheine, added to the apoprotein by ACP phosphodiesterase, which thus plays the same role that it does in coenzyme A. ACP is involved in every step of the fatty acid synthetic process.
amyloid p. See amyloid.
androgen binding p. (ABP) a p. secreted by testicular Sertoli cells along with inhibin and müllerian inhibiting substance. Androgen binding p. probably maintains a high concentration of androgen in the seminiferous tubules.
antitermination p. a p. that permits RNA polymerase to transcribe through certain termination sites.
antitumor p. a p. that inhibits tumor growth.
antiviral p. (AVP) a human or animal factor, induced by interferon in virus-infected cells, which mediates interferon inhibition of virus replication.
autologous p. any p. found normally in the fluids or tissues of the body.
basic p.'s p.'s that are rich in basic amino acids; e.g., histones.
Bence Jones p.'s p.'s with unusual thermosolubility found in the urine of patients with multiple myeloma, consisting of monoclonal immunoglobulin light chains. See Bence Jones reaction. See also immunoglobulin.
bone Gla p. (BGP) osteocalcin
p. C a vitamin K-dependent plasma p. that inhibits coagulation by enzymatic cleavage of the activated forms of factors V and VIII, and thus interferes with the regulation of intravascular clot formation; a deficiency of p. C leads to impaired regulation of blood coagulation. There is an autosomal dominant deficiency [MIM*176860] that, like antithrombin III deficiency and plasminogen deficiency, is associated with an increased risk of severe or premature thrombosis.
cAMP receptor p. (CRP) catabolite (gene) activator p
capping p.'s p.'s that bind to one end of actin filaments, preventing both addition and loss of actin monomers.
catabolite (gene) activator p. (CAP) a p. that can be activated by cAMP, whereupon it affects the action of RNA polymerase by binding it with it or near it on the DNA to be transcribed.cAMP receptor p., catabolite gene activator;
cholesterol ester transport p.'s a p. that transports cholesterol esters from HDL to VLDL and LDL; a deficiency of this protein is associated with elevated HDL cholesterol.
cis-acting p. a p. that acts on the molecule of DNA from which it was expressed.
compound p. conjugated p
conjugated p. p. attached to some other molecule or molecules (not amino acid in nature) otherwise than as a salt; e.g., flavoproteins; chromoproteins, hemoglobins. See also prosthetic group. Cf. simple p. compound p;
copper p. a p. containing one or more copper ions; e.g., cytochrome c oxidase, phenol oxidase.
corticosteroid-binding p. transcortin
C-reactive p. (CRP) a beta-globulin found in the serum of various persons with certain inflammatory, degenerative, and neoplastic diseases; although the p. is not a specific antibody, it precipitates in vitro the C polysaccharide present in all types of pneumococci.
denatured p. a p. whose characteristics or properties have been altered in some way, as by heat, enzyme action, or chemicals, and, in so doing, has lost its biological activity.
derived p. a derivative of p. effected by chemical change, e.g., hydrolysis.
docking p. in the process of translating p.'s that are to be secreted from the cell, translation is arrested until the growing polypeptide chain that is complexed by a specific particle (signal recognition particle) comes in contact with this integral p. of the endoplasmic reticulum.
encephalithogenic p. an important protein in the central nervous system.myelin p. A1;
extrinsic p.'s peripheral p.'s
fatty acid binding p. Z-p
fibrous p. any insoluble p., including the collagens, elastins, and keratins, involved in structural or fibrous tissues.
foreign p. a p. that differs from any p. normally found in the organism in question.heterologous p;
G p.'s intracellular membrane-associated p.'s activated by several (e.g., beta adrenergic) receptors; they serve as second messengers or transducers of the receptor-initiated response to intracellular elements such as enzymes to initiate an effect. These p.'s have a high affinity for guanine nucleotides and hence are named "G" p.'s.G-p., GTP binding p.'s;
G-p. G p.'s
globular p. any p. soluble in water, usually with added acid, alkali, salt, or ethanol, and roughly so classified (albumins, globulins, histones, protamines), in contrast to fibrous p.
GTP binding p.'s G p.'s
heat shock p.'s (hsp) specific p.'s whose synthesis is increased immediately after sudden elevation of temperature; their function is to help diminish the harmful effects of high temperature.
heterologous p. foreign p
homologous p.'s p.'s having a very similar primary, secondary, and tertiary structure.
immune p. antibody
integral p.'s p.'s that cannot be easily separated from a biomembrane.intrinsic p.'s;
intrinsic p.'s integral p.'s
iron-sulfur p.'s p.'s containing one or more iron atoms that are linked to sulfur bridges and/or sulfur of cysteinyl residues; e.g., certain p.'s in the electron transport pathway.
p. kinases a class of enzymes that phosphorylates other p.'s; many of these kinases are responsive to other effectors (e.g., cAMP, cGMP, insulin, epidermal growth factor, calcium and calmodulin, calcium and phospholipids, etc.).
M p. 1. Streptococcus M antigen See also beta-hemolytic streptococci, under streptococcus, Streptococcus pneumoniae. 2. monoclonal immunoglobulin
macrophage inflammatory p. (mak´ro-faj in´flam-ma-to-re) a member of the chemokine family that is chemotactic for certain lymphocyte subsets such as T cytotoxic cells.
matrix Gla p. (MGP) a calcium binding p.
microtubule-associated p.'s (MAPs) p.'s that have a specific association with a- and/or beta-tubulin; e.g., tau, MAP1, MAP2; several have been found in the plaques observed in Alzheimer's disease.
mild p. protein a complex prepared by the reaction of p. oxide with either gelatin or serum albumin. Black shiny crystals liberate p. and it was formerly widely used as a topical anti-infective on mucous membranes. Contains from 19 to 25% p., only a small fraction of which is ionizable. Can produce black or brown pigmentation due to deposition of reduced p. in the tissues.argyrol, silvol;
monoclonal p. monoclonal immunoglobulin
monocyte chemoattractant p.-1 (MCP-1) (mon´o-sIt ke´mo- a-trak´tant) secreted by endothelial cells of a blood vessel wall; it induces extravasation of monocytes.
muscle p.'s p.'s present in muscle.
myelin p. A1 encephalithogenic p
myeloblastic p. See human leukemia-associated antigens, under antigen.
native p. the concept of a p. in its natural state, in the cell, unaltered by heat, chemicals, enzyme action, or the exigencies of extraction.
neutrophil activating p. (NAP) interleukin-8
non-heme iron p. any p. containing iron but not any heme iron; e.g., NADH dehydrogenase.
nonspecific p. a p. substance that elicits a response not mediated by specific antigen-antibody reaction.
odorant binding p. p.'s in nasal mucus that bind lipophilic odor-producing molecules and transfer them to the olfactory receptors. Similar p.'s may mediate taste.
parathyroid hormonelike p. (PLP) a 140 amino acid p. secreted by some cancer cells; it causes hypercalcemia.
pathological p.'s See paraprotein.
peripheral p.'s p.'s that can be easily removed from a biomembrane (e.g., by altering the pH or the ionic strength).extrinsic p.'s;
phenylthiocarbamoyl p. formed by the reaction of phenylisothiocyanate with a terminal a-amino group of a peptide or p. See also phenylisothiocyanate, phenylthiohydantoin.PhNCS p., PTC p;
PhNCS p. phenylthiocarbamoyl p
p. phosphatases a class of enzymes that catalyze the dephosphorylation of specific phosphorylated p.'s.
placenta p. human placental lactogen
plasma p.'s dissolved p.'s (more than 100) of blood plasma, mainly albumins and globulins (normally 6 to 8 g/100 ml); they hold fluid in blood vessels by osmosis and include antibodies and blood-clotting p.'s.serum p.'s;
prion p. small, infectious proteinaceous particle, of non-nucleic acid composition because of its resistance to nucleases; the causative agent, either on a sporadic, genetic, or infectious basis, of six neurodegenerative diseases in animals, and four in humans; the latter include the spongiform encephalopathies of kuru, Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker syndrome and fatal familial insomnia. The gene encoding for the PrP is found on chromosome 20.prion;
protective p. antibody
PTC p. phenylthiocarbamoyl p
purified placental p. human placental lactogen
receptor p. an intracellular p. (or p. fraction) that has a high specific affinity for binding a known stimulus to cellular activity, such as a steroid hormone or adenosine 3´,5´-cyclic phosphate.
retinol-binding p. a plasma p. that binds and transports retinol.
S p. the major fragment produced from pancreatic ribonuclease by the limited action of subtilisin, which cleaves the ribonuclease between residues 20 and 21; the smaller fragment (residues 1-20) is S peptide.
p. S a vitamin K-dependent antithrombotic p. that functions as a cofactor with activated p. C.
serum p.'s plasma p.'s
simple p. p. that yields only a-amino acids or their derivatives by hydrolysis; e.g., albumins, globulins, glutelins, prolamines, albuminoids, histones, protamines. Cf. conjugated p.
stimulatory p. 1 (SP1) an RNA polymerase II transcription factor in vertebrates; binds to DNA in regions rich in G and C residues; a general promoter-binding factor necessary for the activation of many genes.
strong silver p. See strong silver protein.
structure p.'s p.'s whose role is for structure and support in tissue and within the cell; e.g., the collagens.
Tamm-Horsfall p. See Tamm-Horsfall mucoprotein.
thyroxine-binding p. (TBP) 1. thyroxine-binding globulin 2. thyroxine-binding prealbumin
unwinding p.'s enzymes that uncoil the DNA allowing recombination events to occur.
vitamin D-binding p. (DBP) a plasma p. that binds vitamin D.
whey p. the soluble p. contained in the whey of milk clotted by rennin; e.g., lactoglobulin, a-lactalbumin, lactoferrin.
Z-p. a fatty acid-binding protein that participates in the intracellular movement of fatty acids.fatty acid binding p;


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