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Measurement of 1-aspartamido-beta-N-acetylglucosamine amidohydrolase activity in human tissues.

ABSTRACT: The activity of 1-aspartamido-beta-N-acetylglucosamine amidohydrolase (aspartylglucosylaminase, EC 3.5.1.26) was measured in normal and diseased human liver, brain and kidney. Organs from patients with aspartylglucosaminuria show very little activity. Crude homogenates of human organs show a reaction catalysed by a complex enzyme system. With homogenate, the formation of product was linear with time up to about 6 h. Reaction times longer than 6-7h resulted in a decrease in the total concentration of product. This phenomenon was not found with the partially purified enzyme fraction. Linearity of the enzyme activity with different protein concentrations was found, independent of the incubation time. Longer incubation of the crude homogenate resulted in the utilization of the product, N-acetylglucosamine. This phenomenon was not observed with the partially purified enzyme fraction. This amidase from human organs differs from that obtained from other sources and apparently represents a rather complex enzyme system.

SUBMITTER: Dugal B

PROVIDER: S-EPMC1164658 | biostudies-other | 1977 Apr

REPOSITORIES: biostudies-other

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Purification and some properties of 1-aspartamido-beta-N-acetylglucosamine amidohydrolase from human liver.

Project description:Human liver 1-aspartamido-beta-N-acetylglucosamine amidohydrolase (aspartylglucosylaminase, EC 3.5.1.26) was purified 17 500-fold to apparent homogeneity as judged from polyacrylamide-gel disc electrophoresis. A pH optimum of 7.7-9.0 was found. The Km value was pH- and temperature-dependent. At 37 degrees C and pH 7.7, Km was 0.16 mM and it increased to 0.29 at pH 6.0 and 0.23 at pH 9.0. At 25 degrees C and pH 7.7, a Km value of 0.99 mM was obtained. When the substrate concentration was varied, apparent Michaelis-Menten kinetics were obtained. p-Hydroxymercuribenzoate, glutathione or cysteine had no effect on the enzyme activity; 5 mM-N-acetylcysteine inhibited about 47% of the total enzyme activity. Apart from Cu2+, other bivalent ions were virtually ineffective at 1 mM. The kinetic study differentiates this enzyme from aspartylglucosylaminase from other sources.

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Effect of different compounds on 1-aspartamido-beta-N-acetylglucosamine amidohydrolase from human liver.

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Distribution, purification and properties of 1-aspartamido-beta-N-acetylglucosamine amidohydrolase.

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