cAMP-dependent protein kinase I, a unique allosteric enzyme

cAMP-dependent protein kinases are known to be activated by dissociation. There are two types of these enzymes in the mammalian cytosol with similar catalytic subunits but regulatory subunits. With enzymes of type I, ATP counteracts the activation by cAMP. Recent studies of the binding sites of these enzymes for these ligands are reviewed.     

Evaluation of the fluorescein diacetate (FDA) vital dye viability test with hamster and bovine embryos

A study was undertaken to determine: (1) the potential toxicity of a fluorogenic vital dye, fluorescein diacetate (FDA), on hamster and bovine pre-implantation embryos; and (2) whether a correlation exists between the fluorescence of an embryo and its ability to continue development.For the toxicity trial, hamster eight-cell embryos were randomly assigned to one of three groups (control, FDA+UV light or UV light only), and early bovine blastocysts to either a control or FDA+UV light group. Embryos were cultured for 24 h and scored for development to the blastocyst stage. Embryos of both species developed equally well in vitro regardless of whether or not they had been exposed to FDA and UV light. Treated and untreated control embryos from both species were transferred to synchronized recipients. Similar numbers of pregnancies resulted after transfer of treated and untreated embryos from both species.In the second experiment, the proportions of fluorescing embryos were compared using two groups of hamster eight-cell embryos: (1) freshly collected embryos; and (2) cultured embryos that failed to develop. Significantly more of the fresh eight-cell embryos fluoresced than did the cultured, undeveloped embryos. No false negative results were obtained (embryos that developed but failed to fluoresce). However, approximately half of the non-developing, cultured embryos showed varying degrees of fluorescence (false positive). Embryos showing “false positive” fluorescence may be viable, but incapable of further development due to deficiencies of the culture medium.The procedures used in the FDA viability assay were not detrimental to development of late cleavage stage mammalian embryos and thus seem suitable for rapid screening of manipulated embryos for potential damage. However, further work is needed to establish the significance of the false positive results encountered in this study.     

Ethanol stimulates formation of leukotriene C4 in rat gastric mucosa

Ethanol-induced gastric mucosal damage is characterized by microcirculatory changes such as stasis and plasma leakage. Sluggish blood flow and stasis have also been observed after administration of exogenous leukotriene (LT) C4. The effect of ethanol on the release of LTC4 from rat gastric mucosa was therefore investigated. It was found that intragastric instillation of ethanol increases gastric mucosal release of LTC4 in a dose- and time-dependent manner parallel to the production of gastric lesions. The lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the anti-ulcer drug carbenoxolone (CX) inhibited mucosal release of LTC4 and simultaneously protected against gastric damage caused by ethanol. It is concluded that increased formation of LTC4 and/or other 5-lipoxygenase-derived products of arachidonate metabolism may be involved in ethanol-induced gastric damage. Furthermore, inhibition of the 5-lipoxygenase pathway may be an important mechanism of action of gastric protective drugs.