Analysis of the ACP1 gene product: Classification as an FMN phosphatase

Kimberley R. Fuchs, Laurie L. Shekels, David A. Bernlohr

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The relationship between the ACP1 gene product, an 18kDa acid phosphatase (E.C. postulated to function as a protein tyrosyl phosphatase, and the cellular flavin mononucleotide (FMN) phosphatase has been examined in vitro and by using cultured Chinese hamster ovary (CHO) cells. Kinetic analysis indicated that at pH 6 the acid phosphatase utilized a variety of phosphate monoesters as substrates. While small molecules such as FMN were effectively utilized as substrates (kcat/Km = 7.3 × 103 s-1M-1), the tyrosyl phosphorylated form of the adipocyte lipid binding protein was a relatively poor substrate (kcat/Km = 1.7 × 10-1 s-1M-1) suggesting a role for the phosphatase in flavin metabolism. Fractionation of CHO cell extracts revealed that 90% of the FMN phosphatase activity was soluble and that all of the soluble activity eluted from a Sephadex G-75 column with the acid phosphatase. All of the soluble FMN phosphatase activity was inhibited by immunospecific antibodies directed against the bovine heart ACP1 gene product. These results suggest that the ACP1 gene product functions cellularly not as a protein tyrosyl phosphatase but as a soluble FMN phosphatase.

Original languageEnglish (US)
Pages (from-to)1598-1605
Number of pages8
JournalBiochemical and Biophysical Research Communications
Issue number3
StatePublished - Dec 30 1992

Bibliographical note

Funding Information:
The authors would like to thank the members of the Bemlohr laboratory for many helpful discussions and in particular Dr. Ronald Sha and Anne J. Smith for assistance with cell culture and reviewing this manuscript. Dr. Robert L Van Etten is acknowledged for kindly providing the anti-bovine heart acid phosphatase antibody. This work was supported in part by funds to D.A.B. from the Juvenile Diabetes Foundation (JDF 191110).


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