2′-Carboxy-D-arabinitol 1-phosphate (2CA1P), a natural inhibitor of ribulose 1,5-bisphosphate carboxylase was synthesized from 2′-carboxy-D-arabinitol 1,5-bisphosphate (2CABP). The selective dephosphorylation of 2CABP with either acid phosphatase or alkaline phosphatase was investigated by using 31P n.m.r. The n.m.r. spectra of the progress of the reactions indicated that both phosphatases preferentially removed the 5-phosphate from the bisphosphate. After the consumption of all of the bisphosphate, alkaline phosphatase generated a mixture of 2′-carboxy-D-arabinitol 1- and 5-monophosphates in the ratio of about 4:1, along with Pi. The enzyme also hydrolysed the monophosphates to 2′-carboxyarabinitol, thus decreasing the yield of 2CA1P further. In contrast, acid phosphatase catalysed almost quantitative conversion of 2CABP into 2CA1P, preferring to hydrolyse only the 5-phosphate. In either case, separation of the 2CA1P from Pi or other products of enzymic hydrolysis was readily accomplished by conventional ion-exchange chromatography or h.p.l.c.

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