変異蛋白質の質量分析による検出
−臨床検査への応用−
清 水 章*
Detection and Identification of Variant and Abnormally Modified Proteins by Soft Ionization Mass Spectrometry, Unrivaled Technique for Clinical Diagnosis
Akira SHIMIZU, MD*
Using the unique preparation and detection techniques we devised for application of proteins to soft ionization mass spectrometry, we found many variant and abnormally modified proteins. Up to end of 2002, we have diagnosed 96 cases of variant hemoglobins(Hb), which include 45 different and 3 new species. We have diagnosed or confirmed the molecular weight difference of 64 cases of variant transthyretins (TTR), which include 14 different and 3 new species. We found the first 2 cases showing homozygote of TTR 119Thr→Met, a high frequent non-amyloid variant among some European ethnicities. Variants of Cu, Zn-superoxide dismutase, 5 cases, 5 different species, were analyzed and the differences of molecular weight suggested by DNA analyses were confirmed. These are listed in the text.
Cysteine 10 in TTR is modified in vivo and in vitro. We found a marked increase in s-sulfonated TTR in 4 patients with molybdenum cofactor deficiency and homocysteine conjugated TTR in 2 patients with methylene H4 folate reductase deficiency. The carbohydrate deficient transferrin was
detected in 3 cases of carbohydrate deficient glycoprotein syndrome. The
detection of these modified structures might be expected to be a new diagnostic
index for these diseases, which are easily misdiagnosed.
The improved reference method for HbA1C measurement was established using isotope(deuterium) labeled glycated
and non-glycated hexapeptides from amino terminal of Hb β-chain. We checked
the discrepancies of HbA1C values by the routine method and the reference method we established. Most samples containing variant Hbs did not show correct HbA1C values by HPLC and some did not show correct values by immunoassay. We showed a typical example of an enormous increase in the glycation degree because of the amino acid substitution, which was shown clearly by electrospray ionization/mass spectrometry. (Nine figures and 4 tables were selected from 45 slides presented in the lecture.)
[Rinsho Byori 51 : 29〜42, 2003]
*Department of Clinical Pathology, Osaka Medical College, Takatsuki 569-8686
【Key Words】soft ionization mass spectrometry(ソフトイオン化質量分析)，abnormal hemoglobin(異常ヘモグロビン)，transthyretin variant(トランスサイレチンバリアント)，Cu/Zn-superoxide dismutase variant(銅/亜鉛スーパーオキシドジスムターゼ)，HbA1C
*大阪医科大学病態検査学教室中央検査部(〒569-8686 高槻市大学町2-7)
E-mail :shimizu@poh.osaka-med.ac.jp