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Cholecystokinin
Cholecystokinin (CCK or CCK-PZ; from Greek ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac (gallbladder)'') is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. Cholecystokinin, previously called ''pancreozymin'', is synthesized and secreted by enteroendocrine cells in the duodenum,〔(【引用サイトリンク】website=http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/gi/cck.html )〕 the first segment of the small intestine, and causes the release of digestive enzymes and bile from the pancreas and gallbladder, respectively. It also acts as a hunger suppressant. Recent evidence has suggested that it also plays a major role in inducing drug tolerance to opioids like morphine and heroin, and is partly implicated in experiences of pain hypersensitivity during opioid withdrawal.
==Structure==
CCK is composed of varying numbers of amino acids depending on post-translational modification of the ''CCK'' gene product, preprocholecystokinin. Thus CCK is actually a family of hormones identified by number of amino acids, e.g., CCK58, CCK33, CCK22 and CCK8. CCK58 assumes a helix-turn-helix configuration. Its existence was first suggested in 1905 by the British physiologist Joy Simcha Cohen. CCK is very similar in structure to gastrin, another of the gastrointestinal hormones. CCK and gastrin share the same five amino acids at their C-termini.
Most CCK peptides have a sulfate-group attached to the tyrosine in position 7 in the C-terminus. This modification is crucial for the ability of CCK to activate the cholecystokinin A receptor. Nonsulfated CCK peptides also occur, which consequently cannot activate the CCK-A receptor.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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