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Biomedical subjects

H C Neu

Publications and source records attributed to H C Neu.

At least 469 records · Page 26Linked to original sources
PubMed1969

Effect of beta-lactamase location in Escherichia coli on penicillin synergy.

Resistance to ampicillin in Escherichia coli is due generally to the presence of a beta-lactamase (penicillinase). Resistant strains have been found to fall into two groups: those with high-level resistance (1,000 mug/ml or greater) and those with low-level resistance (8 to 250 mug/ml). Most of the high-level resistant organisms posses beta-lactamases whose synthesis is episomally mediated. These strains release penicillinase from the cell when they are subjected to osmotic shock. Low-level resistant strains do not release the enzyme with osmotic shock. High-level resistant strains are not susceptible to the synergistic action of a penicillinase-resistant penicillin with ampicillin. Seventy eight per cent of low-level resistant strains are susceptible to the synergistic action of ampicillin and oxacillin. The two types of beta-lactamases are similar in regard to most properties; both enzymes are subject to competitive inhibition by penicillinase-resistant penicillins. The difference in location in the cell might explain why only some strains of E. coli are susceptible to the synergistic action of penicillin combinations.

Ampicillin↗
PubMed1969

Surface localization of Escherichia coli 5'-nucleotidase by electron microscopy.

The 5'-nucleotidase of Escherichia coli was shown to be located at the cell wall surface by histochemical techniques utilizing the deposition of inorganic phosphate. Penetration of the 5'-nucleotidase in the periplasmic space was seen only in cells treated with ethylenediaminetetraacetic acid (EDTA)-tris(hydroxymethyl)aminomethane (Tris). The 3'-nucleotidase of E. coli was also found to have a surface location, and periplasmic precipitation of inorganic phosphate was seen only after EDTA-Tris-sucrose exposure.

Cell Wall↗
PubMed1968

The 5'-nucleotidases and cyclic phosphodiesterases (3'-nucleotidases) of the Enterobacteriaceae.

All members of the Enterobacteriaceae possess distinct 5'-nucleotidases and cyclic phosphodiesterases (3'-nucleotidases) that can be differentiated from the acid and alkaline phosphatases and the acid sugar hydrolases. The nucleotidases and cyclic phosphodiesterases of the various Enterobacteriaceae are remarkably similar in properties. All of the 5'-nucleotidases hydrolyze 5'-nucleotides, adenosine triphosphate, and uridine diphosphoglucose. Their pH optimum is from 5.7 to 6.1. The cyclic phosphodiesterases hydrolyze 3'-nucleotides, cyclic phosphonucleotides, bis-(p-nitrophenyl)phosphate, and p-nitrophenylphosphate. Their pH optimum is from 7.2 to 7.8. For both enzymes, cobalt showed optimal metal stimulation. An intracellular protein inhibitor for the 5'-nucleotidase is present in all of the Enterobacteriaceae. No inhibitor of cyclic phosphodiesterase activity exists, although hydrolysis of both cyclic phosphonucleotides and 3'-nucleotides is inhibited by ribonucleic acid. Neither of the enzymes is subject to control by phosphate level or by catabolite repression. Of the other bacteria studied, only Haemophilus and Bacillus subtilis contained significant 3'- or 5'-nucleotidase activity.

Bacillus subtilis↗