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Enzyme variants in normal and neoplastic intestinal mucosa
Author(s) -
Trotta Paul P.,
Balis M. Earl
Publication year - 1977
Publication title -
cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.052
H-Index - 304
eISSN - 1097-0142
pISSN - 0008-543X
DOI - 10.1002/1097-0142(197711)40:5+<2592::aid-cncr2820400931>3.0.co;2-e
Subject(s) - adenosine deaminase , isoelectric point , enzyme , isoelectric focusing , biology , microbiology and biotechnology , biochemistry , adenosine , intestinal mucosa , cycloheximide , medicine , protein biosynthesis
Previous work from the Laboratory of Cell Metabolism; Memorial Sloan‐Kettering Cancer Center, has shown that several enzymes exist as different variants in dividing and nondividing cells of the normal intestinal mucosa. We have undertaken a study of the properties of the enzyme adenosine deaminase, which is found in high levels in the intestines of many species, including man. Normal rat colon has been shown to possess predominantly one electrophoretic variant. Tumors induced with methylazoxymethanol show the appearance of a new form with a lower isoelectric point. The normal colon enzyme and the two tumor variants can be distinguished by relative substrate specificity and sensitivity to inhibition by 9‐erythro‐(2‐hydroxy‐3‐nonyl) adenine. These data provide support for the clinical application of combinations of adenosine deaminase inhibitors with cytotoxic adenosine analogs in the chemotherapy of colon carcinoma. This enzyme from normal jejunum has been resolved by both preparative and analytical isoelectric focusing into two variants that exhibit pI values of ca 4.85 (ADase I) and 4.80 (ADase II). The relative proportions of these two forms are markedly different in mitotically active and differentiated cells. The form with the higher isoelectric point predominates in the tip cells. These variants can also be resolved by molecular exclusion chromatography since the apparent molecular weight of ADase I is somewhat higher than that of ADase II (ca 37,000 and 33,500, respectively). The specific adenosine deaminase activity in tip cells is also several‐fold higher than that in the crypt regions. Cycloheximide, a protein synthesis inhibitor, dramatically decreases the activity in the tip. It also changes the normal relative proportions of the two forms so that ADase I is no longer a major form in the tip cells. Thus, the appearance of ADase I in the differentiated cells must be related to a mechanism involving protein synthesis. We conclude that changes in the properties of adenosine deaminase may be closely related to normal growth and differentiation in the intestines.