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Target inactivation analysis was used to measure the functional size of uridine diphosphogalactose: N-acetylglucosamine beta(1,4)galactosyltransferase (galactosyltransferase), cytidine monophospho-N-acetyl-neuraminic acid: beta-galactoside alpha(2,6) sialytransferase (sialyltransferase), and uridine diphosphatase (UDPase) in Golgi membranes isolated from rat liver. The size of nucleoside diphosphatase (NDPase), an enzyme similar to UDPase but localized in rat liver endoplasmic reticulum, was also estimated by target inactivation analysis. The related enzymes, UDPase and NDPase, have target sizes of 96 +/- 4 and 77 +/- 3 kDa, while galactosyltransferase and sialyltransferase have target sizes of 97 +/- 10 and 130 +/- 20 kDa, respectively. The target inactivation sizes of galactosyltransferase and of sialyltransferase are about twice the monomer molecular weights of these enzymes obtained from sedimentation studies of the solubilized membranes as well as those predicted from previously reported cDNA sequences. We conclude from our studies that galactosyltransferase and sialyltransferase probably function as dimers in the Golgi membrane.
We analyzed 11 H. pylori isolates from humans using the artificial chromogenic substrate paranitrophenylphosphorylcholine to detect phospholipase C (PLC) activity. The range of PLC in sonicates was 8.8-92.3 (Mean 56.9 +/- 6.5) nmol of substrate hydrolysed min-1 mg-1 protein; the amount of activity was not associated with urease or cytotoxin levels. Addition of sorbitol or glycerol enhanced PLC activity of H. pylori sonicate and purified PLC from C. perfringens (PLC1) but not purified PLC from B. cereus (PLC3). H. pylori sonicates had little acid phosphatase and no detectable alkaline phosphatase activity, and H. pylori PLC showed markedly different biochemical characteristics from either phosphatase. In total, these studies indicate that activity measured in H. pylori sonicate by PLC assay is due to PLC and not phosphatase activity. The temperature optimum for PLC activity of H. pylori sonicate was 56 degrees C and for PLC 1 was 65 degrees C. For H. pylori PLC and PLC1, optimal activity occurred at pH 8. Despite multiple similarities between H. pylori PLC and PLC1, known PLC inhibitors show different interactions with each enzyme. Although PLC activity is present in many subcellular constituents of H. pylori, including culture supernatants and water extracts, highest specific activity is associated with a membrane-enriched fraction.