| signal peptide | A peptide present on proteins that are destined either to be secreted or to be membrane components. It is usually at the N terminus and normally absent from the mature protein. Normally refers to the sequence (ca 20 amino acids) that interacts with signal recognition particle and directs the ribosome to the endoplasmic reticulum where co translational insertion takes place. Could also refer to sequences that direct post translational uptake by organelles. Signal peptides are highly hydrophobic but with some positively charged residues. The signal sequence is normally removed from the growing peptide chain by signal peptidase, a specific protease located on the cisternal face of the endoplasmic reticulum. See: signal recognition particle. (18 Nov 1997) |
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| signal peptide p25-subunit IV cytochrome oxidase | <chemical> Similar in action to melittin Synonym: p25 presequence peptide-cytochrome oxidase, pre-ctox p25 (26 Jun 1999) |
| signal peptides | Additional polypeptide sequence of 25 to 30 residues at the amino-terminal or carboxy-terminal end of proteins. The signal sequence signals the cellular fate or destination of a newly synthesised protein directing it to its ultimate destination in the cell. These leaders are recognised by the signal recognition particle and bound by specific receptor sites on the outer surface of the endoplasmic reticulum. They are then transported into the cisterna of the endoplasmic reticulum and from there directed to their ultimate destination in the cell. In prokaryotes, the signal peptides attach to the plasma membrane. These signal sequences are ultimately removed by specific peptidases. (12 Dec 1998) |
| signal processing, computer-assisted | Computer-assisted processing of electric, ultrasonic, or electronic signals to interpret function and activity. (12 Dec 1998) |
| signal response coupling | The cascade of processes by which an extracellular signal (typically a hormone or neurotransmitter) interacts with a receptor at the cell surface, causing a change in the level of a second messenger for example calcium or cyclic AMP) and ultimately effects a change in the cells functioning (for example: triggering glucose uptake or initiating cell division). Can also be applied to sensory signal transduction, for example of light at photoreceptors. (18 Nov 1997) |
| signal sequence | A peptide present on proteins that are destined either to be secreted or to be membrane components. It is usually at the N terminus and normally absent from the mature protein. Normally refers to the sequence (ca 20 amino acids) that interacts with signal recognition particle and directs the ribosome to the endoplasmic reticulum where co translational insertion takes place. Could also refer to sequences that direct post translational uptake by organelles. Signal peptides are highly hydrophobic but with some positively charged residues. The signal sequence is normally removed from the growing peptide chain by signal peptidase, a specific protease located on the cisternal face of the endoplasmic reticulum. See: signal recognition particle. (18 Nov 1997) |
| signal-to-noise ratio | <microscopy> Also sometimes used as an abbreviation for serial number, can be somewhat confusing in the case of electronic equipment. (05 Aug 1998) |
| signal transduction | The cascade of processes by which an extracellular signal (typically a hormone or neurotransmitter) interacts with a receptor at the cell surface, causing a change in the level of a second messenger for example calcium or cyclic AMP) and ultimately effects a change in the cells functioning (for example: triggering glucose uptake or initiating cell division). Can also be applied to sensory signal transduction, for example of light at photoreceptors. (18 Nov 1997) |
| signal void | In magnetic resonance imaging, a region emitting no radiofrequency signal, either because there are no activated protons in the region (such as flowing blood) or because a different element predominates, particularly calcium. (05 Mar 2000) |
| nuclear localization signal | Short, predominantly basic amino acid sequences identified as nuclear import signals for some proteins. These sequences are believed to interact with specific receptors at nuclear pores. (12 Dec 1998) |
| acetoacetyl-acyl carrier protein synthase | <enzyme> E coli enzyme, that catalyses condensation of malonyl-acyl carrier protein plus acetyl-acyl carrier protein; not inhibited by cerulenin Registry number: EC 2.3.1.- Synonym: acetoacetyl-acp synthase (26 Jun 1999) |
| acid soluble spore protein | <molecular biology> A DNA binding protein in the spores of some bacteria, thought to stabilise the DNA in an A configuration, so protecting it from cleavage by enzymes or UV light. (18 Nov 1997) |
| acute-phase protein | <haematology> These plasma proteins (in addition to fibrinogen) increase 25% or more in response to inflammation and injury are under direct control of interleukin-6 (IL-6) (hepatocyte-stimulating factor). Other proteins which increase are ceruloplasmin, C3 and C4 which increase 50% or more; alpha-1 acid glycoprotein, alpha-1 antitrypsin, haptoglobin and fibrinogen (the major determinant of viscosity 1 ) which increase two- to fourfold; C-reactive protein (CRP) and serum amyloid A which increase several hundred-fold. Despite long-held clinical opinion to the contrary, available data indicate that neither ESR nor measurement of specific acute-phase reactants are useful in excluding underlying infection or inflammation regardless of the pretest probability. These proteins are secreted into the blood in increased or decreased quantities by hepatocytes in response to trauma, inflammation, or disease. They can serve as inhibitors or mediators of the inflammatory processes. Certain acute-phase proteins have been used to diagnose and follow the course of diseases or as tumour markers. See also: amyloid, c-reactive protein, erythrocyte sedimentation rate, viscosity. (25 Jun 1999) |
| acyl-(acyl-carrier-protein)-phospholipid acyltransferase | <enzyme> Catalyses the formation of phosphatidylethanolamine from acyl-acyl carrier protein and 2-acyl-sn-glycero-3-phosphoethanolamine Registry number: EC 2.3.1.40 Synonym: 2-acyl-gpe acyltransferase, 2-acylglycerophosphoethanolamine acyltransferase (26 Jun 1999) |
| acyl-(acyl-carrier-protein)-UDP-N-acetylglucosamine acyltransferase | <enzyme> E coli enzyme involved in lipid a biosynthesis; uses beta-hydroxymyristoyl-acyl carrier protein to form udp-3-monoacyl-n-acetylglucosamine; amino acid sequence given in second source Registry number: EC 2.3.1.129 Synonym: udp-aguatransferase, lpxa protein, udp-n-acetylglucosamine-3-acyltransferase, udp-n-acetylglucosamine 3-o-acyltransferase, udp-3-o-(r-3-hydroxymyristoyl)glucosamine-n-acyltransferase, lpxd protein, fira gene product, fira protein (26 Jun 1999) |