Abstract
A method for the preparation of highly purified β-hexosaminidase isozymes A and B from human placenta is presented. The purified enzymes possess identical molecular weight and exhibit similar kinetic parameters with artificial fluorogenic substrates. Both enzymes catalyze the hydrolysis of Tay-Sachs ganglioside (Cer-Glc-Gal(NeuAc)-GalNAc) and the corresponding asialo-derivative (Cer-Glc-Gal-GalNAc). Both enzymes are composed of four subunits with a mass of 33,000 daltons each. The enzymes seem to differ only in the interactions of these subunits to form the fully associated enzyme by hydrophobic association and the formation of disulfide bonds. It is possible to convert hexosaminidase A into hexosaminidase B by heating under carefully controlled conditions. The newly formed B has the ion exchange properties and subunit interactions characteristic of highly purified hexosaminidase B isolated from fresh tissue. This conversion does not depend on the removal of N-acetylneuraminic acid. Thus, the two hexosaminidases seem to exist as conformers of each other. A model for the relationship of hexosaminidases in normal tissues and in the various clinical conditions which are characterized by the absence of one or more of these enzymes (Tay-Sachs disease and its variant forms) is presented. A benign form of hexosaminidase A deficiency is postulated based on the ability of both A and B to catalyze the hydrolysis of Tay-Sachs ganglioside.
Highlights
A method for the preparation of highly purified @-hexosa- A appears to be able to cleave this ganglioside while hexosaminidase isozymes A and B from human placenta is pre- minidase B was previously considered to be inactive in this sented
Some of the properties of tissues and in the various clinical conditions which are partly purified enzymes have been described (3) but the activity characterized by the absence of one or more of these en- of these enzymes with the natural substrate GhlZ and the interzymes (Tay-Sachs disease and its variant forms) is pre- relationship of the enzymes have not been studied in a systematic sented
We hope to provide a basis for understanding the relationship of hexosaminidases A and B in normal humans and their alteration in patients with the classic and variant forms of Tay-Sachs disease
Summary
GAL WITH THE TECHKICAL ASSISTANCE OF GEORGE E. MOOK From the Developmental and Metabolic Neurology Branch, National Institute of Neurological Diseasesand Stroke, National Institutes of Health, Bethesda,Maryland 2001~
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