Mechanism of reversible glycine cleavage reaction in Arthrobacter globiformis. Function of lipoic acid in the cleavage and synthesis of blycine. |
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Authors: | H Kochi G Kikuchi |
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Institution: | Department of Biochemistry, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106 USA |
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Abstract: | The physical and chemical characterization of horse serum butyrylcholinesterase has been extended. The results show that the enzyme is a glycoprotein containing about 20% carbohydrate by weight. Mannose, glucosamine, galactose, and sialic acid are the sugar residues found. The extinction coefficient of butyrylcholinesterase, E1cm1% at 280 nm, was found to be 15.2 ± 0.3 by dry weight determination. The molecular weight of the protein in dilute phosphate buffer was determined to be (31.7 ± 1.2) × 104 by high speed equilibrium sedimentation with a redetermined partial specific volume of 0.723 ± 0.003 ml/g. Subunit molecular weights for the dissociated protein were found to be (7.9 ± 0.4) × 104 and (8.1 ± 0.1) × 104, respectively, in guanidine hydrochloride and in a solution at pH 11.8. The subunit molecular weight was also estimated to be (8.8 ± 0.2) × 104 by analytical sodium dodecyl sulfate-gel electrophoresis. This apparently higher subunit molecular weight from dodecyl sulfate gels is expected for glycoproteins containing significant amounts of carbohydrate. No free sulfhydryl group was detected, even though there are six half-cystines in each subunit. Therefore, it seems likely that there are three pairs of disulfide bonds per subunit. The available data indicate that native butyrylcholinesterase is a tetrameric glycoprotein consisting of subunits of equal molecular weight. |
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Keywords: | Recipient of Public Health Service Research Career Development Award GM-14252 from the National Institute of General Medical Sciences To whom correspondence should be addressed |
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