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At least 541 records · Page 30Linked to original sources
PubMed1994

The transglycosylation reaction of cyclodextrin glucanotransferase is operated by a Ping-Pong mechanism.

A new photometric assay of the disproportionation activity of cyclodextrin glucanotransferase (CGTase) using 3-ketobutylidene-beta-2-chloro-4-nitrophenyl-maltopentaoside as the donor, proved that the transglycosylation reaction of CGTase was operated by a Ping-Pong Bi Bi mechanism. The values of the kcat/Km(acceptor) proved that the same configurations of free hydroxyl groups with those of D-glucopyranose at C2, C3 and C4 positions were required for the acceptors used by CGTase. The structure around C6 on acceptors was not essential for acceptor function, but it was recognized by CGTase, since the values of kcat/Km for D-xylose were smaller than that for D-glucose. The value of kcat/Km for maltose was about 20-times larger than that for D-glucose, indicating that at least two glucopyranosyl rings are recognized by the acceptor binding sites.

Bacillus↗
PubMed2006

A new and efficient entry to D-xylo-hexos-4-ulose and some derivatives thereof through epoxidation of the 3,4-hexeno derivative of diacetone-D-glucose.

A new preparation of D-xylo-hexos-4-ulose (1) and of its 3-m-chlorobenzoate (2) has been devised using the epoxidation of 3-deoxy-1,2:5,6-di-O-isopropylidene-D-erythro-hex-3-enofuranose (6) as the key step. The epoxidation of 6 in CH2Cl2 furnished with high yield 1,2:5,6-di-O-isopropylidene-3-O-m-chlorobenzoyl-4-C-hydroxy-D-xylo-hexos-4-ulo-1,4-furanose as a mixture of C-4 hemiacetal anomers (7a,b), which, on acid hydrolysis, gave a tautomeric mixture of 3-O-m-chlorobenzoyl-D-xylo-hexos-4-ulose (2) with an overall 60% yield from 6. The formation of 4-C-methoxy-diacetone-D-glucose derivatives (11a,b) through epoxidation-methanolysis of 6, took place with reduced yield because of the competition between m-chlorobenzoic acid (MCBA) and methanol to the opening by attack at C-4 of the intermediate epoxide and the formation of acyclic products arising from the alternative nucleophilic attack at C-1. Acid hydrolysis of derivatives 11 gave D-xylo-hexos-4-ulose (1) with a 35% overall yield from 6. NMR analysis showed that 2 is composed, in CD3CN, mainly by a 7:3 mixture of 4-keto-alpha- and beta-pyranose forms, while 1, in D2O, is present as a more complex mixture constituted mainly by 4-keto-alpha- and beta-pyranoses and their respective hydrates in a 17:15:34:34 ratio.

Acetone↗
PubMed1968

The kinetics of selective biological transport. 3. Erythrocyte-monosaccharide transport data.

The simplest biological transport system so far extensively investigated is that of monosaccharides in human erythrocytes. Despite its simplicity there is still considerable doubt and divergence of opinion concerning its mechanism. Some confusion may arise as a result of the comparison of diverse data obtained by different workers using a variety of experimental techniques. To minimize this problem, an attempt is made here to repeat, under standard conditions and with as much care as possible, five of the more definitive types of experiments previously performed on this system. It is hoped that the result of this effort is an internally consistent set of data with which the quantitative predictions of various proposed mechanisms may be compared as a primary criterion for their acceptability.

Biological Transport↗