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B E Terzaghi

Publications and source records attributed to B E Terzaghi.

5 recordsLinked to original sources
PubMed1986

Ribulose 1,5-bisphosphate carboxylase. Effect on the catalytic properties of changing methionine-330 to leucine in the Rhodospirillum rubrum enzyme.

Oligonucleotide-directed mutagenesis of cloned Rhodospirillum rubrum ribulose bisphosphate carboxylase/oxygenase with a synthetic 13mer oligonucleotide primer was used to effect a change at Met-330 to Leu-330. The resultant enzyme was kinetically examined in some detail and the following changes were found. The Km(CO2) increased from 0.16 to 2.35 mM, the Km(ribulose bisphosphate) increased from 0.05 to 1.40 mM for the carboxylase reaction and by a similar amount for the oxygenase reaction. The Ki(O2) increased from 0.17 to 6.00 mM, but the ratio of carboxylase activity to oxygenase activity was scarcely affected by the change in amino acid. The binding of the transition state analogue 2-carboxyribitol 1,5-bisphosphate was reversible in the mutant and essentially irreversible in the wild type enzyme. Inhibition by fructose bisphosphate, competitive with ribulose bisphosphate, was slightly increased in the mutant enzyme. These data suggest that the change of the residue from methionine to leucine decreases the stability of the enediol reaction intermediate.

Base Sequence↗
PubMed1978

Effect of Lactose Concentration on the Efficiency of Plating of Bacteriophages on Streptococcus cremoris.

The efficiency of plating of phages derived by ultraviolet induction of, or by lytic growth on, certain strains of Streptococcus cremoris was found to vary by as much as 10 depending on the lactose concentration of the medium in which the indicator bacteria were grown and the length of time the stationary-phase indicator cultures were aged. This effect was noted only when the culture was used as an indicator for phages that had previously grown on an apparently unrelated strain of bacteria. Conditions of culturing and aging had no detectable effect upon the ability of a strain to serve as an indicator for phage that had previously been cultured on the same strain. These observations suggest the presence of some kind of physiologically labile restriction system in strains of S. cremoris. The implications of this finding for increasing the sensitivity of the host range test in determining phage susceptibility, whether from induced lysates, whey, or lytic phage stocks, are discussed. It is recommended that, for all such testing, the concentration of lactose in buffered media be increased to such levels as required to obtain a final pH similar to that of a freshly coagulated milk culture, namely, below pH 5.0.

Journal Article↗
PubMed1975

Improved medium for lactic streptococci and their bacteriophages.

Incorporation of 1.9% beta-disodium glycerophosphate (GP) into a complex medium resulted in improved growth by lactic streptococci at 30 C. The medium, called M17, contained: Phytone peptone, 5.0 g; polypeptone, 5.0 g; yeast extract, 2.5 g; beef extract, 5.0 g; lactose, 5.0 g; ascorbic acid, 0.5 g; GP, 19.0 g; 1.0 M MgSO(4).7H(2)O, 1.0 ml; and glass-distilled water, 1,000 ml. Based on absorbance readings and total counts, all strains of Streptococcus cremoris, S. diacetilactis, and S. lactis grew better in M17 medium than in a similar medium lacking GP or in lactic broth. Enhanced growth was probably due to the increased buffering capacity of the medium, since pH values below 5.70 were not reached after 24 h of growth at 30 C by S. lactis or S. cremoris strains. The medium also proved useful for isolation of bacterial mutants lacking the ability to ferment lactose; such mutants formed minute colonies on M17 agar plates, whereas wild-type cells formed colonies 3 to 4 mm in diameter. Incorporation of sterile GP into skim milk at 1.9% final concentration resulted in enhanced acid-producing activity by lactic streptococci when cells were inoculated from GP milk into skim milk not containing GP. M17 medium also proved superior to other media in demonstrating and distinguishing between lactic streptococcal bacteriophages. Plaques larger than 6 mm in diameter developed with some phage-host combinations, and turbid plaques, indicative of lysogeny, were also easily demonstrated for some systems.

Journal Article↗