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Urinary excretion of the organic acids in patients with type I and III glycogenosis was investigated. In all patients with type I glycogenosis, urinary alpha-ketoglutarate concentration ws about 10 times the normal value. alpha-Ketoglutaric aciduria was not improved by the acute or prolonged administration of a large dose of factors for pyruvate- and alpha-ketoglutarate dehydrogenase complex. On the other hand, the level of alpha-ketoglutarate in the urine from type I patients decreased in conjunction with the decrease of plasma lactate and pyruvate concentration after repeated oral glucose loading. Oral citrate loading brought an increased excretion of alpha-ketoglutarate in type I glycogenosis. It is possible that alpha-ketoglutarate dehydrogenase in the rate-limiting step in tricarboxylic acid cycle and in patients with glycogenosis type I, the excessive excretion of alpha-ketoglutarate may be caused by the limited activity of alpha-ketoglutarate dehydrogenase with excessive substrate.

We have prepared a new radiolabeled substrate (N-[3H]acetylglucosamine-glucuronic acid-N-[3H]acetylglucosamine), from hyaluronic acid, for an assay of beta-N-acetylhexosaminidase activity. Using this substrate, we found a striking deficiency of beta-N-acetylhexosaminidase activity in cultured skin fibroblasts and in liver homogenates from patients with Tay-Sachs disease. DEAE-cellulose chromatography at pH 6.0 revealed that both isoenzymes A and B of beta-N-acetylhexosaminidase from normal liver participated in the catabolism of hyaluronic acid. There were, however, major differences in substrate specificities between isoenzymes A and B. Our results indicate that this substrate should be useful for enzymatic diagnosis of Tay-Sachs disease.

Description d'une methode simple de preparation d'un substrat derive de la chondroitine 6 sulphate et de quelques proprietes enzymatiques de la BN acetyl hexoaminidase hepatique dans la maladie de Tay Sachs. L'auteur conclu que le substrat convient pour mesurer l'activite de l'hexoaminidase A sans avoir besoin de separer les isoenzymes, et serait donc utile pour le diagnostic de maladie de Tay Sachs

β- N -Acetylhexosaminidase in normal human serum was separated into four components by DEAE-cellulose chromatography. The first three peaks were all heat stable. Neither conversion from heat-labile to heat-stable components, nor mutual conversion among heat-stable components occurred by heat treatment of serum. Serum hexosaminidase of Tay—Sachs disease patients had a high level of heat-stable components, especially of I 1 and I 2 , and this was similar to that of brain tissue. The activity of each component of a heterozygote of Tay—Sachs disease and Sandhoff's disease was intermediate between the normal and patient levels.

Epithelial cells are readily obtained when the primary culture of skin fibroblasts is established. The major lysosomal hydrolase activities in normal epithelial cells are lower than those in normal fibroblasts. The primary deficiency of lysosomal enzymes can be detected both in epithelial cells and in cultured skin fibroblasts. However, epithelial cells of I-cell disease show only beta-galactosidase deficiency. This result indicates that epithelial cells have different biochemical properties from skin fibroblasts and they may be similar to those of visceral organs. Therefore, cultured epithelial cells seem to be useful for the studies on lysosomal hydrolase deficiencies.

Iduronate sulfatase was purified from human liver for an investigation of the degradative pathway of dermatan sulfate. An overall 80-fold purification was achieved and, more importantly, the preparation was free of alpha-L-iduronidase, beta-glucuronidase, N-acetylgalactosamine 4-sulfate sulfatase (arylsulfatase B) and highly enriched in beta-N-acetylhexosaminidase. The liver enzyme appeared to be composed of several molecular species. The enzyme activity was optimal at pH 4.0 and its Km was 10--20 microM with sulfoiduronyl sulfoanhydromannitol. Chloride was inhibitory at high concentration and among divalent metal ions, only copper was inhibitory. Nitrocatechol sulfate was not a substrate, but did show competitive inhibition. Its Ki for iduronate sulfatase was similar to its Km for arylsulfatase, suggesting a similarity in the substrate binding sites of iduronate sulfatase and arylsulfatases.