Control of glycoprotein synthesis. Purification and characterization of rabbit liver UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I.

UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I catalyzes an essential first step in the conversion of high mannose to hybrid and complex N-glycans (Schachter, H. (1986) Biochem. Cell Biol. 64, 163-181; Oppenheimer, C.L., and Hill, R.L. (1981) J. Biol. Chem. 256, 799-804), i.e. the addition of GlcNAc to (Man alpha 1-6(Man alpha 1-3)Man alpha 1-6)(Man alpha 1-3)Man beta 1-4GlcNAc-OR to form (Man alpha 1-6(Man alpha 1-3)Man alpha 1-6)(GlcNAc beta 1-2Man alpha 1- 3)Man beta 1-4GlcNAc-OR. The enzyme has been purified from Triton X-100 extracts of rabbit liver by chromatography on CM-Sephadex, Affi-Gel blue, UDP-hexanolamine-Sepharose, and a novel adsorbent in which UDP-GlcNAc is linked to thiopropyl-Sepharose at the 5-position of uracil. The enzyme exists in crude liver extracts in two molecular weight forms separable on Sephadex G-200. The low molecular weight form was purified 64,000-fold with a specific activity of 19.8 mumol/min/mg. The pure enzyme was free of N-acetylglucosaminyltransferase II-V activities. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a single major band of Mr 45,000 and two minor bands of Mr 54,000 and 50,000. All three bands showed retarded elution from an affinity column in which the acceptor substrate for the transferase was covalently linked to Sepharose. Kinetic analysis indicated a largely ordered sequential mechanism with UDP-GlcNAc binding to the enzyme first and UDP leaving last. Studies with synthetic analogues of the substrate Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc showed that an unsubstituted equatorial hydroxyl on carbon 4 of the beta-linked Man residue was essential for enzyme activity.

Anaesthetic-induced increase in ionised calcium in blood mononuclear cells from malignant hyperthermia patients.

The cytoplasmic concentration of ionised calcium, [Ca2+]i, is believed to be altered by agents that induce a malignant hyperthermia (MH) crisis in susceptible individuals. MH patients were identified by the halothane and halothane/caffeine contracture tests done in isolated muscle biopsy specimens. [Ca2+]i was measured in isolated peripheral blood mononuclear cells from MH patients and controls by means of the fluorescent calcium ion indicator quin2. In the absence of halothane there was no significant difference in [Ca2+]i in cells from normal and MH patients. Addition of halothane (4 microliter/ml) significantly increased [Ca2+]i in cells from MH patients but not in controls. The halothane-induced increase in [Ca2+]i required extracellular calcium ions. This is the first evidence of the mechanism of action of halothane in cells of MH patients; the differential effect of halothane on [Ca2+]i might constitute the basis for a non-invasive screening test for MH.

Differentiation of sarcoplasmic reticulum during cardiac myogenesis.

The composition and function of fetal and mature sheep cardiac sarcoplasmic reticulum membranes were investigated. Phospholamban, a major phosphoprotein in the mature sarcoplasmic reticulum membranes, was present in early stages of cardiac myogenesis. This fetal form of phospholamban was phosphorylated by cAMP-dependent protein kinase but not in the presence of Ca2+ and calmodulin. Ca2+ uptake and Ca2+-dependent ATPase activity were low in fetal sarcoplasmic reticulum compared with the adult controls, although the apparent affinities for Ca2+ were similar. Sarcoplasmic reticulum vesicles isolated at all developmental stages had very low levels of plasma membrane (as determined by Na+-K+-ATPase and Na+-Ca2+ exchanger activities) and mitochondrial contamination. Sarcoplasmic reticulum Ca2+ uptake and Ca2+-dependent ATPase activities were not affected by micromolar concentrations of vanadate, and the accumulated Ca2+ could not be released by the addition of NaCl. The amount of both the 110- and 55-kDa protein bands, identified with specific antibodies as Ca2+-ATPase and calsequestrin, respectively, was low in early stages of cardiac myogenesis. Age-related differences in the Ca2+ transport properties of cardiac sarcoplasmic reticulum and in the amount of the Ca2+-ATPase and calsequestrin may explain alterations in the regulation of intracellular Ca2+ concentrations in the fetal heart. This may contribute to the developmental changes in myocardial function.

Changes in cytoplasmic free calcium caused by halothane. Role of the plasma membrane and intracellular Ca2+ stores.

Malignant hyperthermia is a muscle disease characterized by an abnormal response to anaesthetics, stress, and exercise. It is typified by muscle contracture and a dramatic elevation in body temperature. A defect in the regulation of the concentration of cytoplasmic free calcium, [Ca2]i, is thought to underlie this disease, but the actual [Ca2+]i was not measurable until recently. We have shown that the anaesthetic halothane increases [Ca2+]i in isolated lymphocytes from malignant hyperthermia-susceptible humans and pigs but not in the normal counterparts. In this report we extend these observations to a larger number of cases and analyze the molecular mechanisms responsible for the increase. The halothane-mediated rise in [Ca2+]i required external Ca2+ and was prevented by nifedipine, an inhibitor of the voltage-sensitive Ca2+ channels of the cell membrane. In addition, the effect of halothane on the releasable Ca2+ from intracellular stores was determined by measuring the size of the releasable pool before and after addition of the anaesthetic. After addition of halothane, about 73% of this Ca2+ pool was still available for release by the Ca2+ ionophore ionomycin in cells from normal humans and pigs. In contrast, only about 45% of the free Ca2+ in intracellular stores was left after treatment with halothane in cells from malignant hyperthermia-susceptible humans and swine. These results indicate that halothane acts both at the cell membrane and at intracellular organelles, and that this action results in a net increase in [Ca2+]i in malignant hyperthermia, but not in normal cells. The action at the cell membrane appears to be on the voltage-sensitive Ca2+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Labelling of the human erythrocyte glucose transporter with 3H-labelled cytochalasin B occurs via protein photoactivation.

Irradiation of human erythrocyte membranes with 3H-labelled cytochalasin B results in specific photolabelling of the glucose transporter. The action spectrum of photolabelling has a maximum at approx. 280 nm, whereas the absorption spectrum of cytochalasin B is maximal at 210 nm. By irradiating with narrow-band-width light centered at 280 nm for 2 h, 8% of the transporters become covalently labelled and 47% of the remaining cytochalasin B-binding sites are obliterated. We conclude that photolabelling driven by narrow-bandwidth irradiation proceeds via photoactivation of an aromatic amino acid residue on the transporter molecule, and when compared to wide-bandwidth irradiation, permits more efficient incorporation of the label without causing additional photodamage to the remaining transporters.

Phase I trial of mitoxantrone by 24-hour continuous infusion.

Mitoxantrone (DAD) is a new agent which intercalates into DNA. Preclinical studies have demonstrated activity equal to or greater than that of doxorubicin in all tumor systems tested. In this phase I clinical trial, the schedule of drug administration consisted of a 24-hour continuous iv infusion repeated at 21-day intervals. Twenty-nine patients received a total of 66 courses over a dose range of 4-15 mg/m2. The dose-limiting toxic effect was leukopenia, with a wbc count nadir on Day 12 and resolution prior to Day 21. Other toxic effects were thrombocytopenia, mild phlebitis, and blue discoloration of veins. Objective tumor responses were seen in a patient with adenocarcinoma of the breast and in another patient with clear cell carcinoma of the vagina. An additional six patients with acute leukemia were treated at a dose of 12 mg/m2; a decrease in peripheral blast count was observed in four of these six patients. The toxicity of DAD by 24-hour iv infusion was similar to that previously reported for iv bolus administration. We recommend phase II evaluation of DAD at a dose of 12 mg/m2 by single iv injection at 21-day intervals. Patients with acute leukemia should be evaluated at higher dose levels.

Adriamycin analogues. Preparation and biological evaluation of some novel 14-thiaadriamycins.

Condensation of 14-bromodaunorubicin with thiols in methanol, in the presence of potassium carbonate, resulted in the formation of 14-thia analogues of the antitumor antibiotic adriamycin. However, similar condensation of N-(trifluoroacetyl)-14-iododaunorubicin with thiols invariably led to a redox reaction, with the formation of N-(trifluoroacetyl)daunorubicin and disulfides. Accordingly, N-(trifluoroacetyl)-14-bromodaunorubicin was used for reaction with thiols to yield thia analogues of the clinically active but non-DNA-binding adriamycin analogue N-(trifluoroacetyl)adriamycin 14-valerate (AD 32). Reaction of 14-bromoadunorubicin with alpha, omega-alkanedithiols gave bis(thiaadriamycin) analogues as potential difunctional intercalating agents. The aforementioned products, plus two related phenylselena derivatives, were examined for in vitro growth inhibition, in vivo antitumor activity, and, where appropriate, DNA binding. A number of agents, most notably 14-(carbethoxymethyl)-14-thiaadriamycin and N-(trifluoroacetyl)-14-phenyl-14-selenaadriamycin, were active against murine L1210 leukemia in vivo. Several of the amino glycoside unsubstituted 14-thiaadriamycin analogues exhibited DNA-binding properties equivalent to those of adriamycin.

Pharmacologic studies with radiolabeled N-trifluoroacetyladriamycin-14-valerate (AD 32). Comparison of total anthracycline fluorescence and radioactivity in mouse serum and urine.

In connection with pharmacologic studies with AD 32, isotopically-labeled drug prepared from 1-[14C]-trifluoroacetic anhydride and adriamycin-14-valerate was used to determine murine serum and urine levels of radioactivity. Other studies, performed in parallel, measured serum and urinary total fluorescence. Serum fluorescence disappeared in a biphasic pattern, with an initial rapid rate of disappearance followed by a somewhat slower phase. For the first hour, serum radioactivity levels were not significantly different than those measured by fluorescence. After this, however, serum radioactivity decayed at a much slower rate than did fluorescence. Furthermore, a large fraction of the injected radioactivity was found excreted in the urine, whereas urine accounted for only a small fraction of the fluorescence. These results suggest the formation, in part, of a hitherto unrecognized nonfluorescent metabolite, most probably N-trifluoracetyldaunosamine.

Comparative metabolism and excretion of adriamycin in man, monkey, and rat.

Adriamycin and its fluorescent metabolites in bile (man, monkey, and rat) and urine (man and monkey) were determined by means of a simple, rapid, and highly reproducible high-performance liquid chromatographic procedure. Species differences in metabolism and biliary excretion were observed with respect to aldoketo reductase and conjugase activities.

Hepatobiliary metabolism and excretion of adriamycin and N-trifluoroacetyladriamycin-14-valerate in the rat.

In connection with mechanism of action studies with N-trifluoroacetlyadriamycin-14-valerate (AD 32), a superior Adriamycin (ADR) analog under development in these laboratories, serial bile samples were collected from male Sprague-Dawley rats given a single i.v. dose of either ADR (4 mg/kg) or AD 32 (20 mg/kg) and were analyzed for anthracyclines by thin-layer chromatography-fluorometry and high-performance liquid chromatography. For ADR, 20% of the administered dose was accounted for at 24 hr, whereas 80% of the AD 32 dose were excreted into the bile by this time. ADR underwent little biotransformation; 80% of the 48-hr cumulative fluorescence excretion was attributable to unchanged drug, one-half the remainder was adriamycinol, and the balance was polar conjugates. In contrast, AD 32 underwent extensive metabolism to N-trifluoracetyladriamycin, N-trifluoroacetyladriamycinol, and polar conjugates, mostly glucuronides of N-trifluoroacetyladriamycin and N-trifluoroacetyladriamycinol. Based on direct and indirect evidence, ADR was not a metabolite of AD 32.