PubMed Health⌕ Search

Biomedical subjects

H M Kalckar

Publications and source records attributed to H M Kalckar.

At least 37 records · Page 2Linked to original sources
PubMed1979

Selective high metabolic lability of uridine, guanosine and cytosine triphosphates in response to glucose deprivation and refeeding of untransformed and polyoma virus-transformed hamster fibroblasts.

Sugar deprivation of hamster fibroblasts (NIL) affected the steady state levels (pool sizes) of cellular acid soluble nucleotides in the folloing fashion: the pools of UTP, GTP and CTP decreased to a much greater extent than the cellular ATP pools, with the UTP pools undergoing the most dramatic reduction. Sugar deprivation of polyoma-transformed NIL cells (PyNIL) yielded even sharper decreases in the nucleoside triphosphate pools with relative changes similar to those of the untransformed cells. Inhibition of protein synthesis by cycloheximide, initiated at the onset of (and continued during) sugar deprivation, prevented the reduction in pool sizes and yielded values slightly higher than those observed for pool sizes in cells cultured in sugar-supplemented medium. Refeeding glucose to sugar-depleted hamster fibroblasts led to rapid increases (within 1 hour) in the UTP and CTP pools to levels well above the pool sizes observed in cells which were continuously cultured (16 hours) in sugar supplemented medium. Feeding NIL or PyNIL cells with fructose instead of glucose as the only hexose source did not appreciably affect any of the ribonucleoside triphosphate pool sizes. Measurements of hexose uptake by NIL and PyNIL cells under a variety of conditions suggest that hexose transport is not regulated by the total cellular pools of ATP or any of the other ribonucleoside triphosphates.

Animals↗
PubMed1979

Uncouplers of oxidative phosphorylation promote derepression of the hexose transport system in cultures of hamster cells.

Long-term (18-24 hr) preincubation of NIL hamster cell cultures with D-glucose or D-glucosamine (both of which repress the hexose transport system) gave rise to a striking loss of the hexose transport system ("super-repression") when cycloheximide was also present in the culture medium. However, if 0.2 mM 2,4-dinitrophenol (DNP) was also present, the cycloheximide-mediated super-repression was prevented. Moreover, the presence of DNP at this low concentration contributed to an increase in hexose uptake such that it was substantially higher than that permitted by either of the two repressive sugars alone. When the cultures were maintained in medium containing D-fructose in place of glucose, a marked increase in uptake occurred, and this increase (derepression) was not affected by DNP. The derepression due to glucose deprivation and the increases caused by DNP treatment were also observed when 3-O-methylglucose was used to measure hexose transport. Although cultures maintained in the presence of glucosamine exhibited a repressed hexose transport rate, they did not generate significant amounts of lactic acid. DNP, and other uncouplers of oxidative phosphorylation, promoted a derepressed state of hexose transport but did not stimulate the generation of lactate from glucosamine. These data suggest that the metabolic repression phenomena of hexose transport do not depend on glycolysis but rather on the "energized" state of the cell. The energized state of the cell may also be required for the super-repression of hexose transport that is especially apparent when protein synthesis is blocked by cycloheximide.

Animals↗
PubMed1979

Catabolic control of the enhanced alanine-preferring system for amino acid transport in glucose-starved hamster cells requires protein synthesis.

In cultured hamster cells starved for glucose for 24 hr there is an enhancement of the rate of alpha-aminoisobutyric acid transport ("shiftup"). When the starved cells are re-fed with glucose, the rate of transport shifts back down to the low, "regulated" rate typical of cells continuously fed with medium containing glucose ("shiftdown"). The high, deregulated rate of transport is maintained, however, when cycloheximide is present for 24 hr during the re-feeding with glucose. Maintenance of the high transport rate is evident only when the cells are incubated in amino acid-free medium just prior to the transport assay or when the assays are conducted with isolated membrane vesicles. A premature, pseudoshiftdown was observed in intact cells within as little as 2 hr after re-feeding when care was not taken to deplete the amino acid pool prior to the transport assay. In addition, a cycloheximide-insensitive increase in transport was observed when cultures were re-fed for 2 hr with amino acid-free medium containing fresh serum. These results emphasize the often overlooked precautions that should be taken to guard against artifacts that could mislead interpretations of amino acid transport data. More important, however, is the finding that Na(+)-dependent amino acid transport in cultured animal cells is regulated in part by a factor (or factors) that becomes inactivated when the cells are maintained under nonglycolytic culture conditions. In order to reactivate the control mechanism, starved cells that have been re-fed with glucose must resynthesize the regulatory factor(s). Thus, in at least cultured hamster cells, Na(+)-dependent amino acid transport regulation is much like the hexose transport regulation in that catabolic control (shiftdown) requires protein synthesis.

Alanine↗
PubMed1977

Comparative studies of glucose-fed and glucose-starved hamster cell cultures: responses in galactose metabolism.

The metabolic flow of trace amounts of D-[14C]-galactose was followed in cultures of transformed and untransformed hamster cells over a period ranging from five minutes to two hours. The results of chromatographic and enzymatic analyses of the soluble pools are described. Non-glycolytic cells(previously deprived of sugar periods of up to 24 hours) convert D-galactose to galactose-1-phosphate and uridine diphosphoglucuronic acid in 10 to 20 minutes. In the same short assay time, glycolytic cells which have been maintained for 24 hours in media containing glucose or galactose convert D-galactose to uridine diphsphogalactose and uridine diphosphoglucose (ratio 1.4:1). Long term diprivation of sugar also results in 3- to 4-fold increases in the uptake of galactose. In addition, the incorporation of galactose label into chloroformethanol soluble material appears to be influenced by the culture conditions of the untransformed cells while incorporation in the transformed cells appears unaffected. When cycloheximide is included in the maintenance medium for extended periods, the non-glycolytic cells also show increases in galactose uptake rates but the glucose-fed, glycolytic cells llose uptake ability. UDPhexose is the main galactose metabolic peak in the soluble pools of the cycloheximide-treated, glycolytic and the cycloheximide-treated, non-glycolytic cells. The results of these experiments suggests that uptake of galactose and its subsequent metabolism are under separate control.

Animals↗
PubMed1976

The periplasmic galactose receptor protein of Escherichia coli in relation to galactose chemotaxis.

The periplasmic galactose receptor protein of E. coli is the common macromolecule in the initiation of two functions, chemotaxis and active transport. The substrates are glucose and galactose and the affinity for binding to the receptor protein is high (Kp -2 X 10(-8) M for glucose and 1 X 10(-7) M for galactose). A second binding site shows a 100-fold lower affinity. The high concentration of the galactose receptor protein in the periplasmic space tends to give retention through recapture of the ligands. The kinetic properties of the galactose receptor protein are, in general, in harmomy with the kinetics of chemotactic responses to spatial or temporal sugar gradients.

Biological Transport, Active↗
PubMed1973

Carbohydrate catabolism and the enhancement of uptake of galactose in hamster cells transformed by polyoma virus.

Untransformed as well as polyoma virus-transformed hamster cells can be grown equally well on a slow catabolite like galactose as on a rapid catabolite like glucose. The rate of uptake of galactose is greatly enhanced in the transformed cells as compared with untransformed cells, and this enhancement of entry was as markedly expressed in galactose-grown cultures as in glucose-grown cultures. Since the transformed cultures grown in glucose medium consume practically all of their carbohydrate, contrary to the galactose-grown cultures, problems dealing with regulation of transport by substrate concentrations have to be dealt with also. The galactose captured by the cells accumulates initially as galactose, alpha-galactose-1-phosphate, and UDP-galactose. However, after a 24-hr growth on a galactose growth medium, the product accumulated was almost exclusively galactitol. In spite of the enhancement of entry of galactose into the transformed cells, the metabolic pathway becomes stalled even before it has reached the stage of glucose-1-phosphate, largely due to a choke of the enzyme UDP-galactose-4-epimerase (EC 5.1.3.2). Among the sparse amounts of catabolic products generated by the transformed cells from galactose, carbon dioxide (allebeit no D-xylose) and lactic acid were found, both of them in much smaller amounts than seen if glucose is the carbohydrate source. Also, growth of transformed cells on a galactose medium gradually tends to become oriented, a phenomenon that could be called "contact promotion." Subsequent addition of glucose disturbs the oriented growth and interferes with contact promotion.

Animals↗
PubMed1973

Two distinct types of enhancement of galactose uptake into hamster cells: tumor-virus transformation and hexose starvation.

Enhancement of hexose uptake seems well correlated with transformation of cell cultures by tumor viruses and the absence of contact inhibition. Enhancement of sugar uptake has also been observed as a result of hexose starvation. Both types of enhancement can clearly be demonstrated in cultures of hamster cells when uptake of (14)C-labeled galactose is monitored after 10 or 20 min. The profiles of accumulation products are strikingly different. In cultures of hamster NIL cells transformed with polyoma virus much of the (14)C is accumulated as UDPhexose. Untransformed cells accumulate galactose-l-phosphate as well as UDPhexose. Hexose-starved cells show enhanced uptake of galactose; however, this marked enhancement was only observed in NIL cultures close to contact inhibition. The novel and common feature seen in hexose-starved cells when incubated briefly with (14)C-labeled galactose is the occurrence of a marked accumulation of [(14)C]UDPglucuronic acid at the expense of UDPhexose. The ratio [(14)C]UDPglucuronic acid/UDPhexose in cultures fed glucose or galactose was invariably low (0.15-0.2) regardless of the presence or absence of contact inhibition. 20 hr of hexose starvation invariably changed this ratio by a factor of 10 or more, due to accumulation of UDPglucuronic acid. This result was also observed in cultures transformed with polyoma virus. The presence of 3-O-methylglucose in the growth medium did not alter the typical "sugar starvation pattern" (i.e., the UDPglucuronic acid/UDPhexose ratio averaged 1.7). Enhancement of galactose uptake by hexose starvation was very pronounced in NIL cultures that were close to contact inhibition, but was not a prominent feature in the polyoma-transformed cultures. The transformed cells grown on glucose or galactose growth medium showed the usual enhanced rate of uptake of galactose as compared with nontransformed near-confluent cultures that had been fed hexose. The polyoma-induced enhancement showed none of the features characteristic of hexosestarved cells.

Animals↗