Cholecystokinin-converting enzymes in brain.
Crude extracts of porcine cerebral cortical tissue convert cholecystokinin (CCK) to its COOH-terminal fragments, the dodecapeptide (CCK-12) and the octapeptide (CCK-8). The Sephadex G-75 void volume eluate of the crude extract cleaves the arginine-isoleucine bond and effects conversion only to CCK-12; the Sephadex G-50 void volume eluate of the same extract cleaves the arginine-aspartate bond as well, so that both CCK-12 and CCK-8 are end products. Thus, there are at least two enzymes; the one involved in the conversion to CCK-12 is of larger molecular radius than the other. The Km for the cleavage of CCK at the arginine-isoleucine bond by the Sephadex G-75 void volume eluate enzyme is 1.1 X 10(-6) M; the Km for trypsin cleavage of the same bond is 4.7 x 10(-6) M. The lower Vmax for the brain enzyme (1.5 x 10(-11) mol/min per g of extract) compared with trypsin (66 x 10(-11) mol/min per g of trypsin) simply reflects the lesser degree of purify of the brain extract than of the highly purified trypsin.
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002766:Cholecystokinin / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D013379:Substrate Specificity; D013552:Swine; D013997:Time Factors
D010446:Peptide Fragments; D002766:Cholecystokinin; D010447:Peptide Hydrolases