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K Paigen

Publications and source records attributed to K Paigen.

At least 73 records · Page 4Linked to original sources
PubMed1975

Genetic determination of the alpha-galactosidase developmental program in mice.

The expression of alpha-galactosidase in liver, heart, and brain during postembryonic development has been examined in several inbred mouse strains. In most strains, the developmental patterns of alpha-galactosidase are coordinate with those of two other acid hydrolases, beta-glucuronidase and beta-galactosidase. Certain inbred mouse strains, including members of the C57-C58 family, have a tissue-specific alteration in the temporal expression of alpha-galactosidase activity. This alteration shows additive inheritance and appears to be controlled by a single genetic locus. The altered developmental expression of the enzyme is not accompanied by any discernible change in its physical properties.

Animals↗
PubMed1974

Enzyme measurements on single cells.

A simple and sensitive procedure has been developed for enzymatic assays in single cells and applied to the measurement of beta-glucuronidase in single parenchymal cells of liver. Cells deposited in microdroplets under oil were ruptured by freezing and thawing and allowed to react with a fluorogenic substrate. The fluorescence is developed by diffusing an organic base into the droplets and measured in a fluorescence microscope equipped with a photomultiplier.

Animals↗
PubMed1972

Coordinated development of -glucuronidase and -galactosidase in mouse organs.

Changing concentrations of beta-glucuronidase and beta-galactosidase are coordinated during the development of mouse liver, heart, and brain. Although coordinate, the developmental patterns for the two enzymes are under independent control by genetic elements apparently linked to the respective structural genes.

Age Factors↗
PubMed1971

Isolation and characterization of an Escherichia coli bacteriophage requiring cell wall galactose.

A new coliphage, designated U3, has been selected for the ability to discriminate the presence of galactose in the cell wall of Escherichia coli. U3 attacks E. coli K-12 cells that are able to incorporate galactose into their cell walls, but mutants blocked in the synthesis of uridine diphosphogalactose, the precursor of cell wall galactose, are completely resistant to the phage. U3 is a small, tail-less, approximately spherical phage resembling phiX174 in its physical properties. Its diameter by electron microscopy is 21 to 22 nm, and its particle weight is approximately 4 x 10(6) daltons. Like phiX174, U3 appears to have a single-stranded deoxyribonucleic acid genome and has at least four cistrons.

Adsorption↗
PubMed1969

Catabolite inhibition: a general phenomenon in the control of carbohydrate utilization.

When Escherichia coli is grown in synthetic medium with radioactive galactose or lactose as the carbon source, the addition of glucose rapidly inhibited utilization of the radioactive substrate, whether the formation of (14)CO(2) or acid-insoluble products was measured. The inhibition was reversed after the removal of glucose. Experiments with mutants blocked in subsequent steps of galactose and lactose metabolism demonstrated that the inhibition occurs prior to the formation of the first metabolic product. The utilization of a variety of sugars, including maltose, lactose, mannose, galactose, l-arabinose, xylose, and glycerol was inhibited by glucose. Of a number of carbohydrates tested as potential inhibitors, only glucose and, to a lesser extent, glucose-6-phosphate (G-6-P) were capable of inhibiting the utilization of all of the substrates. Glucose did not inhibit G-6-P utilization but G-6-P inhibited glucose utilization. With all substrates, except glycerol, there was a delay before the onset of inhibition by G-6-P. We conclude that E. coli has a general regulatory mechanism, termed catabolite inhibition, which controls the activity of early reactions in carbohydrate metabolism, allowing certain substrates to be utilized preferentially.

Antimetabolites↗
PubMed1969

Relationships between the regulation of the lactose and galactose operons of Escherichia coli.

A group of structurally related compounds, including galactose, fucose, and a number of galactosides, are regulatory effectors for both the lac and gal operons of Escherichia coli. Although a common set of effectors exists, each operon appears to be regulated independently of the other. Experiments with various regulatory mutants have shown, first, that the presence of the proteins of one operon is without effect on the regulation of the other and, second, that the influence an effector has on one operon is independent of the presence or the functional state of the regulatory genes of the other operon. It is unlikely, therefore, that the two operons share a common regulatory macromolecule. Both gal R(-) and gal o(c) regulatory mutants are equally resistant to repression by glucose and galactosides. It has been possible to show, in the gal operon, that induction and repression are competitive processes. For this operon, the differential rate of enzyme synthesis is set by the relative intracellular concentrations of inducer (fucose) and repressor (isopropylthiogalactoside).

Enzyme Induction↗
PubMed1968

Paradoxical effect of weak inducers on the lac operon of Escherichia coli.

Previously, we reported the existence of a group of compounds whose function in the regulation of the lac operon was "paradoxical" in that they acted as either inducers or repressors depending on the circumstances. We now show that this group of compounds does not repress the lac operon by catabolite repression, transient repression, or by preventing the uptake of inducers. A model is presented which shows that "paradoxical" behavior is to be expected if a weak inducer is present at a concentration that is high relative to its binding affinity for the regulatory macromolecule. This model depends on the assumptions that the regulatory macromolecule is an allosteric protein which undergoes a transition between two conformational states and that the rate of enzyme synthesis depends on the fraction of protein molecules in each state. The previous observations on the responses of lac regulatory mutants to weak inducers have been extended to a series of such mutants. Weak inducers repress beta-galactosidase synthesis in several i(-) mutants. When this happens, enzyme synthesis can be reinduced by using a strong inducer such as isopropyl-beta-d-thiogalactoside. These compounds induce operator constitutives and the i(t) mutant more easily than they induce a wild-type strain.

Enzyme Induction↗
PubMed1968

Loss of host-controlled restriction of lambda bacteriophage in Escherichia coli following methionine deprivation.

lambda Bacteriophages produced in Escherichia coli C (designated as lambda . C) are restricted in their ability to grow in E. coli K-12. The rare successful infections that arise in the K-12 population occur in "special" cells which have lost their capacity to restrict lambda . C. These infections yield modified progeny phage (designated as lambda . K) which, unlike lambda . C, plate equally well on E. coli C and E. coli K-12. When methionine, but no other amino acid, was removed from the growth medium of a mutant strain of E. coli K-12, the number of special cells rapidly increased 500- to 3,000-fold. These new special cells retain their capacity to produce modified lambda . K progeny. This conversion of restricting cells into special cells does not require the synthesis of new protein. The special cells formed when methionine was removed from the culture did not revert into restricting cells when methionine was restored. Such cells have also lost the ability to divide for at least 4 hr after methionine supplementation. When methionine was restored, the remaining restricting cells, but not the special cells, immediately resumed growth. Removing methionine from cultures of E. coli B caused a similar increase in the number of special cells able to support the growth of lambda . C and lambda . K. However, when E. coli K-12 (P1) cultures were deprived of methionine, the number of special cells increased for lambda . C but not for lambda . K. Thus, retention of the P1-restriction system, unlike the B- and the K-12-systems, does not require the presence of methionine.

Coliphages↗