GTP-sensitive adenylate cyclases in liver membranes achieved by glucagon and by cholera toxin pretreatment displayed similar responses to added GTP in assay with respect to magnitude and sensitivity. However, their susceptibility to GTP formed during incubation from added GDP catalyzed by membrane-associated nucleoside diphosphate kinase(mNDPK) was different. Adenylate cyclase pretreated with cholera toxin was essentially unaffected by added GDP, while further addition of glucagon produced activation. GTP-stimulated adenylate cyclase activity in toxin-treated membranes was inhibited by added GDP, whereas glucagon addition reduced the inhibitory action of GDP by two orders of magnitude. Since neither pretreatment with toxin nor glucagon addition altered GTP formation by mNDPK, these observations suggest a possible presence of a mechanism by which hormone makes adenylate cyclase susceptible to the GTP formed via mNDPK for activation.

Adenylyl Cyclases↗

PubMed1985

Adenosine 5'-(beta, gamma-imino)triphosphate and guanosine 5'-O-(2-thiodiphosphate) do not necessarily provide non-phosphorylating conditions in adenylate cyclase studies.

Commercial preparations of adenosine 5'-(beta, gamma-imino)triphosphate (App(NH)p) were found to be contaminated with a GTP-like substance(s) as well as a phosphate donor(s) for GDP. Thus, when these preparations were used as substrate with no purification, GDP was as effective as GTP in promoting PGE1 stimulation of human platelet adenylate cyclase. With purified App(NH)p as substrate, the effect of PGE1 with GDP was reduced but still observable, while that with GTP was unaltered. PGE1 also caused a stimulation in the presence of guanosine 5'-o-(2-thiodiphosphate)(GDP beta S) with ATP as substrate. Both of the PGE1-stimulated activities observed with GDP and its analog were completely lost by the addition of UDP, thereby, inhibiting GTP formation catalyzed by membrane-associated nucleoside diphosphate kinase. The results demonstrate that the stimulatory effects of PGE1 observed with GDP and App(NH)p, and with GDP beta S and ATP were transphosphorylation dependent and, therefore, the analogs must be used with special caution in adenylate cyclase studies.

Adenosine Triphosphate↗

PubMed1985

Presence of interferon and antibodies to BK virus in amniotic fluid of normal pregnant women.

Paired samples of maternal sera, umbilical cord sera and amniotic fluids were tested for antibodies to BK virus (BKV) and for interferon content. It was found that two out of 14 pregnant women were antibody negative, the latter were estimated to be susceptible to BKV primary infection. In contrast, there was no foetal case among those which were at risk of foetal infection with BKV as judged from the presence of BKV antibody in maternal sera and interferon in the placentas. It might be hypothesized that BKV may be transmitted to the foetus only in the case of BKV primary infection of antibody-negative pregnant women with undetectable amount of interferon (IFN) in the placenta.

Amniotic Fluid↗

PubMed1985