Periplasmic localization of nicotinate phosphoribosyltransferase in Escherichia coli

Nicotinate phosphoribosyltransferase (NAPRTase) in Escherichia coli mediates the formation of nicotinate mononucleotide, a direct precursor of nicotinamide adenine dinucleotide (NAD), from nicotinate and 5-phosphoribosyl-1-pyrophosphate. Specifically, NAPRTase contributes to NAD synthesis by utilizing intracellular nicotinate formed from NAD degradation products, which are recycled by NAD cycle enzymes and exogenous nicotinate when it is available. In previous studies, it has been tacitly assumed that almost all NAD cycle enzymes are localized in the cytoplasm of E. coli. The results of this investigation provide evidence that NAPRTase is a periplasmic (extracytoplasmic) enzyme. The osmotic shock of exponential-phase cells of E. coli K-12 and ML 308-225 resulted in the release of 63 to 72% and 42 to 48%, respectively, of the NAPRTase into the shock medium. In addition, when exponential cells of strains K-12 and ML 308-225 were converted into spheroplasts, 75 to 84% and 54 to 68%, respectively, of the enzyme was released into the spheroplast medium. Since previous estimates of the effective levels of NAPRTase present in putative repressed and derepressed E. coli cells appeared to be very low, a more convenient and accurate alternative method for the evaluation of NAPRTase in whole cells was developed. The results show that NAPRTase is subject only to a modest degree of enzyme repression. In addition, no evidence was found for the presence of a protein or low-molecular-weight inhibitor of the enzyme in repressed cells.

Control of hepatic bleeding with microfibrillar collagen

Microfibrillar (Avitene) is a new absorbable topical hemostatic agent whose mechanism of action is platelet entrapment and activation of platelet clotting factors. It adheres to moist tissue surfaces to form a firm, flexible hemostatic coagulum. It has been used clinically in 36 patients with hepatic bleeding of diverse etiology, including bleeding from the gallbladder fossa, lacerations, resectional surfaces, biopsy sites, capsular denudations, and hepatic tumors. Although not intended to control major hemorrhage were major vessel ligation or resection is properly indicated, its topical use for diffuse small vessel bleeding may be life-saving. It is exceptionally useful in such conditions as cirrhosis and in thrombocytopenic or thrombasthenic coagulopathies. One treatment failure out of 36 occurred.