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金沢大学医療技術短期大学部, 乳酸脱水素酵素 (LD) アイソザイムの多様性から生ずる活性測定値の試薬間差ないし方法間差を是正するため, 部分精製したLD1を管理物質として, 試料中のアイソザイムLD1活性を測定することを試みた。耐熱菌, ヒト赤血球, ラット心筋のLD抽出液について性状を検討したところ, ラットLD1が熱に安定であり, ヒト血清のLD1と電気泳動易動度, Km値などの物理化学的性状が近似しており, 酵素標準物質として妥当であった。これを標準物質として各種試薬を用い, ヒト血清, 管理用血清の総LD活性およびLD1活性を測定した。乳酸を基質とした試薬間での収束度はLD総活性で0.8～2.0%, LD1活性で0.2～3.6%となり, ピルビン酸を基質とした方法間での収束度はLD総活性で5.8～7.8%, LD1活性で0.7～6.3%となり, 施設問是正における指標としてのLD1活性測定の有用性が示された。, In order to reduce inter-assay variations in the measurement of the activities of lactate dehydrogenase (LD) in sera, we developed a technique to only measure isoenzyme LD1 in sample specimens using purified LD1 as an enzyme reference. We selected the rat LD1 isoenzyme as a reference enzyme after examing various thermostable enzymes, including those from tissue extracts of B. stearothermophilus, rat heart muscle, and human erythrocytes, and comparing their enzymic properties with human serum LD1. After measuring LD1 activities in 5 serum samples and 3 control sera using several commercially available LD assay systems as standards, we compared the coefficient of variation among the measured activity values. When we used LD assay systems with lactate as a substrate, we found that the inter-assay CV for the measurement of total LD and LD1 activities of these sera were 0.8-2.0% and 0.2-3.6%, respectivety. When we used pyruvate as the substrate, the CV were 5.3-7.8% and 0.7-6.3%, respectively. The interassay CV for the measurement of LD1 activities in sera were significantly smaller than that for the total LD activitiesin sera.