Replacing Mn2+ with Co2+ in Human Arginase I Enhances Cytotoxicity toward L-Arginine Auxotrophic Cancer Cell Lines
Replacing the two Mn{sup 2+} ions normally present in human Arginase I with Co{sup 2+} resulted in a significantly lowered K{sub M} value without a concomitant reduction in k{sub cat}. In addition, the pH dependence of the reaction was shifted from a pK{sub a} of 8.5 to a pK{sub a} of 7.5. The combination of these effects led to a 10-fold increase in overall catalytic activity (k{sub cat}/K{sub M}) at pH 7.4, close to the pH of human serum. Just as important for therapeutic applications, Co{sup 2+} substitution lead to significantly increased serum stability of the enzyme. Our data can be explained by direct coordination of L-Arg to one of the Co{sup 2+} ions during reaction, consistent with previously reported model studies. In vitro cytotoxicity experiments verified that the Co{sup 2+}-substituted human Arg I displays an approximately 12- to 15-fold lower IC{sub 50} value for the killing of human hepatocellular carcinoma and melanoma cell lines and thus constitutes a promising new candidate for the treatment of L-Arg auxotrophic tumors.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- DOE - OFFICE OF SCIENCE
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1020148
- Report Number(s):
- BNL-95998-2011-JA; TRN: US201116%%129
- Journal Information:
- ACS Chemical Biology, Vol. 5, Issue 3; ISSN 1554-8929
- Country of Publication:
- United States
- Language:
- English
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