Biochemical properties of thylakoid membrane inorganic pyrophosphatase (PPase) from spinach were investigated in this study. Mg2+ (5 mM) markedly stimulated the PPase activity under alkaline pH values. The native substrate for the hydrolytic reaction Of PPase appeared to be magnesiumpyrophosphate. Among anions investigated, only did F� cause severe inhibition. Illumination had no effect on PPase activity, indicating its independence of photosynthetic electron tramsport and associated energization reactions. The radiation inactivation analysis showed that the functional size of PPase was 86.9 � 4.3 kDa. Group specific modification of enzyme demonstrated the presence of essential sulfhydryl residue at the active site which was embedded in the membrane of thylakoid. 菠菜葉綠餅囊膜上存在有一無機焦磷酸水解酵素。此焦磷酸水解酵素可在鹼性的環境中水解焦磷酸。而焦磷酸水解酵素之水解反應需要鎂離子，故而推測其自然受質是鎂--焦磷酸。在研究陰離子對該酵素活性影響的測試中，發現僅氟離子具強烈的抑制作用。此焦磷酸水解酵素的活性與光合電子傳遞及囊膜能激狀無關。經輻射鈍化分析顯示該酵素在執行焦磷酸水解反應時之功能單位為86.9正負8.4仟道爾吞。利用各種不同化學修飾劑分別對不同官能團進行修飾，發現該酵素在活性中心處含有一半胱胺酸，且深埋於葉綠餅囊膜中。
