HPPD Proposed Reaction
HPPD may refer to: * Hallucinogen persisting perception disorder, a perception disorder that can be caused by hallucinogenic drug use * 4-hydroxyphenylpyruvate dioxygenase, an enzyme found in almost all aerobic life forms and the primary target of some herbicides :*One of those HPPD inhibitor herbicides, a 4-hydroxyphenylpyruvate dioxygenase inhibitor 4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors (HPPD inhibitors) are a class of herbicides that prevent growth in plants by blocking 4-Hydroxyphenylpyruvate dioxygenase, an enzyme in plants that breaks down the amino acid tyrosine into molec ...

Hallucinogen Persisting Perception Disorder
Hallucinogen persisting perception disorder (HPPD) is a non-psychotic disorder in which a person experiences apparent lasting or persistent visual hallucinations or perceptual distortions after a previous use of drugs, including but not limited to psychedelics, dissociatives, entactogens, THC, SSRIs and antibiotics. Despite being designated as a hallucinogen-specific disorder, the specific contributory role of psychedelic drugs is unknown. The hallucinations and perceptual changes consist of, but are not limited to, visual snow, trails and after images (palinopsia), light fractals on flat surfaces, intensified colors, altered motion perception, pareidolia, micropsia, and macropsia. People who have never previously taken drugs have also reported some visual anomalies associated with HPPD (such as floaters and visual snow). HPPD is a DSM-5 diagnosis with diagnostic code 292.89 (F16.983). For the diagnosis to be made, other psychological, psychiatric, or neurological conditions mus ...
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Perception
Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system, which in turn result from physical or chemical stimulation of the sensory system.Goldstein (2009) pp. 5–7 Vision involves light striking the retina of the eye; smell is mediated by odor molecules; and hearing involves pressure waves. Perception is not only the passive receipt of these signals, but it is also shaped by the recipient's learning, memory, expectation, and attention. Gregory, Richard. "Perception" in Gregory, Zangwill (1987) pp. 598–601. Sensory input is a process that transforms this low-level information to higher-level information (e.g., extracts shapes for object recognition). The process that follows connects a person's concepts and expectations (or knowledge), restorative and selective mechanisms (such as ...
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Hallucinogenic Drug
Hallucinogens are a large, diverse class of psychoactive drugs that can produce altered states of consciousness characterized by major alterations in thought, mood, and perception as well as other changes. Most hallucinogens can be categorized as either being psychedelics, dissociatives, or deliriants. However, certain hallucinogens such as Fly agaric as well as other gabaergic hallucinogenics are more often considered to technically be hypnotics, therefore indicating another separate subcategory of drugs which can substantially alter visual perception. Etymology The word ''hallucinogen'' is derived from the word ''hallucination''. The term ''hallucinate'' dates back to around 1595–1605, and is derived from the Latin ''hallūcinātus'', the past participle of ''(h)allūcināri'', meaning "to wander in the mind." Characteristics Leo Hollister gave five criteria for classifying a drug as hallucinogenic.Glennon RA. Classical drugs: an introductory overview. In Lin GC and Glen ...
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4-hydroxyphenylpyruvate Dioxygenase
4-Hydroxyphenylpyruvate dioxygenase (HPPD), also known as α-ketoisocaproate dioxygenase (KIC dioxygenase), is an Fe(II)-containing non-heme oxygenase that catalyzes the second reaction in the catabolism of tyrosine - the conversion of 4-hydroxyphenylpyruvate into homogentisate. HPPD also catalyzes the conversion of phenylpyruvate to 2-hydroxyphenylacetate and the conversion of α-ketoisocaproate to β-hydroxy β-methylbutyrate. HPPD is an enzyme that is found in nearly all aerobic forms of life. Enzyme mechanism HPPD is categorized within a class of oxygenase enzymes that usually utilize α-ketoglutarate and diatomic oxygen to oxygenate or oxidize a target molecule. However, HPPD differs from most molecules in this class due to the fact that it does not use α-ketoglutarate, and it only utilizes two substrates while adding both atoms of diatomic oxygen into the product, homogentisate. The HPPD reaction occurs through a NIH shift and involves the oxidative decarboxylation ...
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