Rapid purification and N-terminal sequencing of a potato tuber cyclic nucleotide binding phosphatase

A high affinity cyclic nucleotide binding phosphatase was purified to homogeneity from potato tubers by a rapid procedure involving batchwise elution from carboxymethylcellulose and gel filtration. The phosphatase has a molecular weight of 28,000 as estimated from both SDS-PAGE and gel filtration. The phosphatase binds to Con A-agarose and is eluted by 0.5 M alpha-methylglucoside. The phosphatase catalyses the hydrolysis of nucleoside monophosphates, p-nitrophenylphosphate and O-phospho-L-tyrosine, but not of O-phospho-L-serine or O-phospho-L-threonine. N-terminal sequencing of the phosphatase has revealed significant homology with two similar-size soybean leaf and stem storage glycoproteins.