ABSTRACT
Two fucsyltransferases (FucT-2 and FucT-3) have been solubilized from Golgi-rich membrane fraction of bovine spleen, using a cationic detergent. FucT-3 was distinguished from FucT-2 by comparing their kinetic parameters and heat stability. FucT-2 and FucT-3 lost activity (85 %) and (5 %), respectively, when heated at 55°C for 10 sec. Two galactosyltransferases (GalT-3 and GalT-4) and two sialyltransferases (SAT-2 and SAT-3) have also been solubilized from embryonic chicken brain membranes using nonionic detergents. Affinity chromatography and microisoelectric focusing were used to separate these enzymes into functionally pure fractions. Anomeric and positional linkages in some of the products (LM1 and LD1c) have also been established. The terminal NeuAc(α2–8) linkage in GD3 and LD1c was established by identification of the partially methylated penultimate [Ac-14C]sialic acid.
ABSTRACT
Multiple forms of ricin have been isolated from castor bean seeds. Two forms, ricin-1 and ricin-2, differ in their isoelectric pI values and toxicity towards IMR- 32 cells. Inhibition of IMR-32 DNA polymerase α2 is more pronounced with ricin-1 (65%) than with ricin-2 (10%). Ricin Β chain (pI = 5.2) isolated from ricin-1 binds to IMR-32 cell surfaces as well as inhibits DNA polymerase α2 activity when studied in vitro. The presence of galβ-linked glycoconjugates near the active site of IMR-32 DNA polymerase α2 has been proposed. Replication modulators which bind to the glycose portion of the enzymes involved in the replication system may need a mandatory binding to cell surface glycoconjugates for their activity.