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PubMed1967

Genetically alterable transport of amethopterin in Diplococcus pneumoniae. II. Impairment of the system associated with various mutant genotypes.

Six mutations determining resistance to amethopterin were examined for their effects on the active transport of the drug. In strains bearing each of the mutations and exhibiting resistance levels varying from 10- to 100-fold, transport at limiting concentrations of H(3)-amethopterin was reduced from 2.5 to 10 times the rate characteristic of the wild type. Kinetic analysis of transport showed an increase in the value for K(m) of the system in all of the mutants. Values for the wild-type system were 0.9 x 10(-6)m and for the mutants varied between 2.5 x 10(-6)m and 9.0 x 10(-6)m. Values for V(max) were approximately the same for each system. The mutant transport systems also exhibited a shift in pH optimum from near 6.0 (wild-type) to below 5.0. The results were interpreted as an alteration in the binding properties of the permease in the mutant strains.

Biological Transport↗
PubMed1968

Purification and properties of mutant and wild-type diaphorases from Diplococcus pneumoniae.

Optochin-resistant mutant and wild-type diaphorases were purified approximately 300-fold by a combination of batch adsorption and column chromatography with diethylaminoethyl cellulose, and were characterized with regard to their pH optima, sensitivity to optochin inhibition and heat inactivation, Michaelis constants with flavine mononucleotide (FMN) and reduced nicotinamide adenine dinucleotide (NADH), and inhibition constants with optochin hydrochloride. The pH optima of the purified diaphorases were similar, but the purified diaphorases from the optochin-resistant strains were approximately four to five times more resistant to heat inactivation at 45 C than was the wild-type diaphorase. Purified diaphorase preparations from the optochin-resistant pneumococci had greater activities per milligram of protein and were more resistant to optochin inhibition than the preparation from the optochin-sensitive pneumococcus. Michaelis constants for FMN and NADH were similar; however, the inhibition constants of the optochin-resistant diaphorases were four to eight times greater than that of the optochin-sensitive diaphorase. Optochin hydrochloride produced a noncompetitive type of inhibition with FMN as substrate but a competitive type of inhibition with NADH as substrate. Optochin hydrochloride produced an approximately 10-fold increase in the Michaelis constant for NADH. The concentration of drug required to produce this effect was, however, greater with the mutant diaphorases than with the wild-type diaphorase. Optochin hydrochloride quenched the fluorescence of riboflavine. This phenomenon did not appear to be related to the diaphorase-inhibitory activity of the drug, however, since the pH requirements of the two reactions were different. Quenching of riboflavine fluorescence by optochin hydrochloride increased with a rise in pH, whereas inhibition of diaphorase activity by optochin hydrochloride was greater at pH 6.8 than at pH 7.6.

Adsorption↗