Abstract
1. An F(-)-insensitive 3'-nucleotidase was purified from spinach leaf tissue; the enzyme hydrolysed 3'-AMP, 3'-CMP and adenosine 3'-phosphate 5'-sulphatophosphate but not adenosine 5'-nucleotides nor PP(i). The pH optimum of the enzyme was 7.5; K(m) (3'-AMP) was approx. 0.8mm and K(m) (3'-CMP) was approx. 3.3mm. 3'-Nucleotidase activity was not associated with chloroplasts. Purified Mg(2+)-dependent pyrophosphatase, free from F(-)-insensitive 3'-nucleotidase, catalysed some hydrolysis of 3'-AMP; this activity was F(-)-sensitive. 2. Adenosine 5'-sulphatophosphate kinase activity was demonstrated in crude spinach extracts supplied with 3'-AMP by the synthesis of the sulphate ester of 2-naphthol in the presence of purified phenol sulphotransferase; purified ATP sulphurylase and pyrophosphatase were also added to synthesize adenosine 5'-sulphatophosphate. Adenosine 5'-sulphatophosphate kinase activity was associated with chloroplasts and was released by sonication. 3. Isolated chloroplasts synthesized adenosine 3'-phosphate 5'-sulphatophosphate from sulphate and ATP in the presence of a 3'-nucleotide; the formation of adenosine 5'-sulphatophosphate was negligible. In the absence of a 3'-nucleotide the synthesis of adenosine 3'-phosphate 5'-sulphatophosphate was negligible, but the formation of adenosine 5'-sulphatophosphate was readily detected. Some properties of the synthesis of adenosine 3'-phosphate 5'-sulphatophosphate by isolated chloroplasts are described. 4. Adenosine 3'-phosphate 5'-sulphatophosphate, synthesized by isolated chloroplasts, was characterized by specific enzyme methods, electrophoresis and i.r. spectrophotometry. 5. Isolated chloroplasts catalysed the incorporation of sulphur from sulphate into cystine/cysteine; the incorporation was enhanced by 3'-AMP and l-serine. It was concluded that adenosine 3'-phosphate 5'-sulphatophosphate is an intermediate in the incorporation of sulphur from sulphate into cystine/cysteine.