Pion
In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: π) is any of three subatomic particles: π0, π+, and π−. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons (and, more generally, the lightest hadrons), because they are composed of the lightest quarks (the u and d quarks). They are unstable, with the charged pions π+ and π− decaying with a mean lifetime of 26 nanoseconds (6992260000000000000♠2.6×10−8 seconds), and the neutral pion π0 decaying with a much shorter lifetime of 6983840000000000000♠8.4×10−17 seconds. Charged pions most often decay into muons and muon neutrinos, and neutral pions into gamma rays.
The exchange of virtual pions, along with the vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but are produced commonly in high energy accelerators in collisions between hadrons. All types of pions are also produced in natural processes when high energy cosmic ray protons and other hadronic cosmic ray components interact with matter in the Earth's atmosphere. Recently, detection of characteristic gamma rays originating from decay of neutral pions in two supernova remnant stars has shown that pions are produced copiously in supernovas, most probably in conjunction with production of high energy protons that are detected on Earth as cosmic rays.
Pion (disambiguation)
A pion is a type of subatomic particle.
Pion may also refer to:
Protein pigeon homolog
Protein pigeon homolog also known as gamma-secretase activating protein (GSAP) is a protein that in humans is encoded by the PION gene.
Gene
The human PION gene is located on the long (q) arm of chromosome 7 at band 11.23, from base pair 76,778,007 to base pair 76,883,653. Highly conserved PION orthologs have been identified in most vertebrates for which complete genome data are available. More distantly related orthologs are also expressed in insects including the pigeon gene in Drosophila melanogaster that when mutated produces the "pigeon" phenotype. The name of the human PION gene derives the corresponding Drosophila gene.
Protein
The transcribed human pigeon homolog protein is 854 amino acid residues in length. A 16 kDa fragment (GSAP-16K) derived from 121 residues from the C-terminus region of the full length protein is known as the γ-secretase activating protein (GSAP).
Function
γ-secretase activating protein (GSAP) increases β-amyloid production through a mechanism involving its interactions with both γ-secretase and its substrate, the amyloid precursor protein (APP). By binding to both the γ-secretase enzyme and its APP substrate, GSAP increases the affinity and the selectivity of the enzyme for this particular substrate.
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