HUMAN RED-CELL ACID-PHOSPHATASE (ACP1) - THE AMINO-ACID-SEQUENCE OF THE 2 ISOZYMES BF AND BS ENCODED BY THE ACP1-STAR-B ALLELE

The pair of isozymes, Bf and Bs, encoded by the human red cell acid phosphatase ACP1*B allele has been sequenced. Similar but not identical primary structures were observed. Both isozymes consist of a single peptide chain of 157 amino acid residues, which is acetylated at the amino-terminal alanine residue. The Bf and Bs isozymes are not glycosylated, and the calculated molecular masses are 17,932 and 17,867 Da, respectively. They are identical except for the sequence segment 40-73, which is peculiar to the respective isozyme. This is consistent with our hypothesis that the two isozymes are generated as the result of alternative splicing of the primary RNA transcript. The finding of a signature sequence offers the basis for the characteristic differences in catalytic and molecular properties of the Bf and Bs isozymes. A high degree of homology was found between the Bs isozyme and the 18-kDa cytosolic acid phosphatase from bovine liver. No homology was observed with other sequenced proteins, and this establishes these low molecular weight acid phosphatases as products of a distinct gene family.