Diadenosine 5‘,5“‘-<em>p</em>,<em>p</em><sup>4</sup>-Tetraphosphate Deficiency in Blood Platelets of the Chédiak-Higashi Syndrome

Diadenosine tetraphosphate (AP4A) is an unusual nucleotide found in a variety of cells, including platelets. It has been suggested that platelet AP4A is stored in the dense granules and is metabolically inactive. We have studied the AP4A content of blood platelets in two patients and three cattle with Chédiak-Higashi syndrome (CHS), a hereditary platelet defect with dense granule deficiency. Acid-soluble extractions of whole blood and platelets were neutralized. The adenosine triphosphate (ATP) level was measured by luminescence technique. To measure the AP4A content, the neutralized extract was treated with phosphomonoesterase for removal of ATP. The AP4A content was then measured by coupling the phosphodiesterase and luciferase reaction. The AP4A content was 0.43 nmol/mg protein for normal human platelets and 0.004 nmol/mg protein for CHS platelets. The ATP/AP4A ratio was 67 for normal and 3,023 for CHS platelets. The whole blood AP4A was reduced by 89% in CHS patients who had only a slight decrease in ATP level (26% reduction). Similarly, bovine platelets with CHS showed a marked decrease of AP4A content and a moderate reduction of the ATP level. The platelet ATP/AP4A ratio was 351 and 3,133 for normal and CHS cattle, respectively. Results demonstrate a marked reduction of AP4A in CHS platelets and suggest that AP4A may be a useful marker for the measurement of dense granule content in platelets.

四磷酸二腺苷（AP4A）是一种在多种细胞（包括血小板）中发现的特殊核苷酸。有人提出血小板中的AP4A储存于致密颗粒中且无代谢活性。我们研究了两名患者和三头患有切迪阿克 - 东综合征（CHS）的牛的血小板中AP4A的含量，CHS是一种伴有致密颗粒缺乏的遗传性血小板缺陷疾病。对全血和血小板进行酸溶性提取后进行中和。采用发光技术测定三磷酸腺苷（ATP）水平。为测定AP4A含量，用磷酸单酯酶处理中和后的提取物以去除ATP。然后通过偶联磷酸二酯酶和荧光素酶反应来测定AP4A含量。正常人血小板的AP4A含量为0.43纳摩尔/毫克蛋白质，CHS血小板为0.004纳摩尔/毫克蛋白质。正常血小板的ATP/AP4A比值为67，CHS血小板为3023。在ATP水平仅有轻微下降（降低26%）的CHS患者中，全血AP4A降低了89%。同样，患有CHS的牛血小板AP4A含量显著降低，ATP水平适度下降。正常牛和患CHS的牛的血小板ATP/AP4A比值分别为351和3133。结果表明CHS血小板中AP4A显著减少，并提示AP4A可能是测量血小板中致密颗粒含量的一个有用标志物。