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Research Communication

Thiamin Is Decomposed Due to Anaphe spp. Entomophagy in Seasonal Ataxia Patients in Nigeria¹

Takahiro Nishimune², Yoshihiro Watanabe^*, Hideki Okazaki and Hiromu Akai^**

Laboratories of Food Hygiene and ^* Large-Scale Catering, Nutrition Research Section, Musashigaoka College, 111 Yoshimi-cho, Hiki-gun, Saitama-ken, 355-0154, Japan, and ^** Nodai Institute, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo, 156-8502 Japan

²To whom correspondence should be addressed.

A fairly high activity of a relatively heat-resistant thiaminase was detected and characterized from the pupae of an African silkworm Anaphe spp. which had been the putative cause of a seasonal ataxia and impaired consciousness in Nigerians. The thiaminase in the buffer extract of Anaphe pupae was type I (thiamin: base 2-methyl-4-aminopyrimidine methyl transferase EC 2.5.1.2), and the optimal temperature and pH were 70°C and 8.0–8.5, respectively. Based on gel filtration chromatography, the molecules were estimated to be 200 kDa. Second substrates which could be utilized by the thiaminase were pyridoxine, amino acids, glutathione, taurine and 4-aminopyridine. Thiamin phosphate esters were inactive as substrates. This is the first report describing an insect thiaminase. Our results indicate the necessity of thorough heat treatment for the detoxification of the African silkworm, making the worm a safe source of high-quality protein.

KEY WORDS: • thiaminase • thiamin • entomophagy • ataxia • silk worm • Anaphe venata

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