Identification of a glycosidase activity with apparent specificity for 2-deoxy-D-glucose in glycosidic linkage.

2-Deoxy-D-glucose (dGlc) is a carbohydrate with significant activity as an inhibitor of glucose metabolism and as a precursor in the synthesis of glycosylated macromolecules; several of the enzymes associated with its metabolism remain uncharacterized. In the present report, the partial purification and some of the properties of a mammalian enzyme that appears to be relatively specific for the hydrolysis of dGlc bound in glycosidic linkage is described. The physiological function of this enzymatic activity is unknown. In addition, dGlc has been shown to be taken up by HTC cells in culture and incorporated into macromolecular bound form, both as dGlc and as 2-deoxygalactose which is formed from dGlc.

Phenylthioalkylamines in experimental tumor treatment in mice.

Two phenylthioalkylamines, phenylthioethylamine (PTEA) and phenylthiopropylamine (PTPA), were prepared and tested for cytotoxicity in vitro and as antitumor agents in (C57BL X DBA/2)F1 (BDF1) mice. Low concentrations of PTEA (median effective concentrations of 8.0, 12.0, and 1.3 micrograms PTEA/ml) inhibited the growth of P388 murine lymphoma, L1210 leukemia, and B16 melanoma cells in culture. PTPA was more effective; concentrations of 0.80, 0.56, and 0.35 micrograms PTPA/ml inhibited the growth of P388, L1210, and B16 in vitro by 50%. PTEA and PTPA treatment increased survival times in BDF1 mice bearing the P388 lymphoma, L1210 leukemia, B16 melanoma, and Lewis lung tumors. Multiple daily administrations of the test compounds were more effective than single daily injections in increasing the life-span in mice bearing the P388 lymphoma and B16 melanoma. Both PTEA and PTPA inhibited the enzyme copper-zinc superoxide dismutase.

Neuraminidase activity and cell surface sialic acid turnover in Rous sarcoma virus transformed chick embryo fibroblasts.

Neuraminidase activity of Rous sarcoma virus transformed chick embryo fibroblasts (RSV-CEF) was assayed using an exogenous substrate, neuraminlactitol-[3H], and endogenous, cell surface [14C]-N]-acetyl-neuraminic acid. RSV-CEF had higher neuraminidase activity toward both substrates than did chick embryo fibroblasts (CEF) or nontransformed, Rous associated virus infected CEF (RAV-CEF). The total sialic acid content of RSV-CEF was lower than CEF or RAV-CEF, and more of the total sialic acid was accessible to extracellular Clostridium perfringens neuraminidase. Activity of the enzymes synthesizing and degrading the substrate for sialyltransferase, cytidine-5'-monophosphate-N-acetyl-neuraminic acid (CMP-AcNeu) was measured in order to determine whether control of substrate levels for sialyltransferase might contribute to the decreased levels of glycoprotein bound sialic acid. No change in activity of these enzymes was found in RSV-CEF as compared to CEF or RAV-CEF.

1-beta-D-arabinofuranosylcytosine nucleotide inhibition of sialic acid metabolism in WI-38 cells.

Because cytidine nucleotides have been demonstrated to affect activity of sialytransferases of both normal and malignant cells, we have investigated the effects of nucleotides of 1-beta-D-arabinofuranosylcytosine (ara-C) [1-beta-D-arabinofuranosylcytosine 5'-monophosphate and 1-beta-D-arabinofuranosycytosine 5'-triphosphate (ara-CTP)] on synthesis of sialoglycoproteins. Normal human diploid fibroblasts (WI-38 cells) were used in culture at confluency, when fewer than 1% of the cells were synthesizing DNA. 1-beta-D-Arabinofuranosylcytosine 5'-monophosphate was inhibitory to both sialytransferase activity of the intact cell and total cell homogenate transferase activity. The enzymes which synthesize and degrade the substrate of sialyltransferases, cytidine 5'-monophosphate-N-acetylneuraminic acid (CMP-AcNeu), were also tested for inhibition by nucleotides of ara-C. Synthesis of CMP-AcNeu was competitively inhibited by ara-CTP; however, formation of CMP-AcNeu when ara-CTP was supplied as substrate could not be detected. Hydrolysis of CMP-AcNeu was inhibited more severely by cytidine 5'-triphosphate than by ara-CTP or 1-beta-D-arabinofuranosylcytosine 5'-monophosphate. Confluent cultures of WI-38 cells exposed to ara-C have decreased amounts of glycoprotein sialic acid, suggesting that ara-C nucleotides may reach sufficient intracellular concentrations to affect the enzyme systems described.

Sialyltransferase activities of aging diploid fibroblasts.

Sialyltransferase activity and cell-cell adhesion rates of aging WI-38 cells were studied to determine the possible basis for a previously described decrease in membrane bound sialic acid and loss of proliferation of senescent cells. Ectosialyltransferase was demonstrated on the surface of both young and old WI-38 cells. The sialyltransferase assays consist of an enzyme source which is either the surface of intact cells (ectoenzyme) or a Triton X-100 cell homogenate, the nucleotide sialic acid donor (cytidine monophosphate-N-acetylneuraminic acid), and an asialo-acceptor which may be endogenous to the enzyme preparation or may be added exogenously. When sialyltransferase activity is measured in the absence of exogenous acceptors, there is a greater amount of sialic acid transferred by odl cells. However, when exogenous acceptors are provided, the amount of transfer is stimulated to a greater extent in young cells equalizing the amount of sialic acid incorporated into young and old cells. This suggests that there are fewer asialoglycoproteins and that acceptor concentration is a limiting factor in assays of young cell sialyltransferase. The end result of this may be the previously described decreased amount of membrane-bound sialic acid of old cells. A change in the adhesiveness of old cells is described which may be related to the altered cell surface.