UDPG-Glucan-Glucosyl-Transferase in Human Polymorphonuclear Leukocytes.

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Abstract
The UDPG:[alpha]-1,4-glucan [alpha]-4-glucosyl-transferaae (transferase) of normal human polymorphonuclear leukocytes was assayed and characterized. The enzyme showed an absolute dependence on the presence of glucose-6-phosphate(G-6-P) and was further stimulated by Mg ions. The Km for the substrate UDPG (with G-6-P present) was 2 x 10-3 [image] without Mg2+ and 6 x 10-4 [image] with Mg2+ in the assay. The activation constant (Ka) for G-6-P was 1.5 x 10-2 [image] without Mg2+ and 1 x 10-3 [image] with Mg2+ present. Normal human polymorphonuclear leukocytes lack the mechanisms for interconversion of the D (G-6-P dependent) and I (G-6-P independent) forms of transferase. The activity of transferase in the presence of G-6-P and Mg2+ ranged from 3.1 to 7.04 [mu]moles of glucose incorporated from UDPG into glycogen per 108 leukocytes in one hour.