Search PubMed⌕ Search

Biomedical subjects

K Budd

Publications and source records attributed to K Budd.

29 records · Page 2Linked to original sources
PubMed1976

Evidence for a negative membrane potential and for movement of C1- against its electrochemical gradient in the ascomycete Neocosmospora vasinfecta.

The iodides of three lipid-soluble cations (dibenzyldimethylammonium; tribenzylmethylammonium, TBMA+; ethyldimethylbenzylammonium) were synthesized by the reaction of 14C-labeled methyl or 14C-labeled ethyl iodide with the appropriate secondary of tertiary amine and used in an attempt to measure the transmembrane electrical potential difference in Neocosmospora. Only mycelium containing high levels of Na+ accumulated measureable amounts of these cations and only above pH 6. Uptake was reduced in the presence of exogenous K+, Na+, Mg2+, or tris(hydroxymethyl)aminomethane. The velocity of TBMA+ uptake was proportional to its concentration between 46 and 427 muM. Neither the rate nor the extent of TBMB+ uptake was greatly affected by the presence of a fivefold excess of either dibenzyldimethylammonium or ethyldimethylbenzylammonium, even though these cations were themselves accumulated. The uncoupler m-chlorophenylhydrazone induced loss of previously accumulated TBMA+ from the mycelium. Anaerobiosis and cold (5 degrees C) temperature both inhibited TBMA+ uptake but did not induce the loss of previously accumulated TBMA+. The uptake of lipophilic cations by Na+-rich mycelium indicated a minimum transmembrane electrical potential of -60 to -70 mV (inside negative). Net uptake of these cations appeared to be strongly influenced by the availability of endogenous exchangeable cations and by the presence of other exogenous cations, as well as by the membrane potential. Despite these limitations, transport of C1- by Na+-rich mycelium appeared to take place against the electrochemical gradient for C1-.

Anaerobiosis↗
PubMed1975

Potassium fluxes in Neocosmospora vasinfecta.

The unidirectional K+ fluxes across the mycelial surface of Neocosmospora vasinfecta were determined using 42K. Influx was mediated by at least two kinetically distinct systems, one having an apparent Km of 6-5 mu-equiv. K+/l and the other of about 1-0 m-equiv. K+/l. The VMAX for both systems was in the range 18 to 22 mu-equiv. K+/100 mg mycelial dry matter/h (1-0 to 1-2 m-equiv. K+/l cell-water/min). Influx was strongly inhibited by 2,4-dinitrophenol, sodium azide, sodium arsenate and anaerobiosis. K+ efflux was dependent on the external K+ concentration and ranged from 3 to 10% of mycelial K+/h. The maximum efflux rate was always considerably less than the initial influx rate for the K+ concentrations examined. During incubation in dilute KCl solutions, K+ influx decreased to a value approaching the K+ efflux rate. It is considered that equilibrium with external K+ is attained primarily by the regulation of K+ influx, and that this may be the principal mechanism controlling cytoplasmic K+ levels. Adsorption of K+ was also observed throughout the K+ concentration range examined and can be attributed to two distinct K+-binding entities at the mycelial surface, half-saturating at approximately O-I mM-and 4-4 mM-KCl respectively.

Adsorption↗
PubMed1975

Halide uptake by the filamentous ascomycete Neocosmospora vasinfecta.

The uptake of Cl minus by the ascomycetes Neocosmospora vasinfecta was investigated. Intramycelial concentrations of more than 55 mM (890-fold the external concentration) were reached. Accumulation was as inorganic Cl minus and nystatin induced total loss of mycelial Cl minus without extensive protein loss, implying that Cl minus retention was not due to binding to macromolecules. Cl minus transport was largely unidirectional with efflux being low under all conditions. Uptake was temperature dependent (maximal Arrhenius activation energy of 18.0 kcal/mol) and was severely reduced by KCN, dicyclohexylcarbodiimide, and anaerobiosis. A comparison with the inhibition of oxygen uptake under the same conditions implied that Cl minus transport was not directly coupled to aerobic electron transport. Cl minus uptake was a saturatable function of the external Cl minus concentration, and apparent Km values of 6.4 times 10-6 M and 10-4 M were calculated. Of the anions tested, only Br minus effectively inhibited Cl minus uptake and I minus, NO3 minus, SO4 minus 2, HCO3 minus, and H2PO4 minus were without effect. Cl minus uptake did not require concomitant cation uptake.

Anaerobiosis↗
PubMed1975

The development of an increased rate of Cl- uptake in the ascomycete Neocosmospora vasinfecta.

Freshly harvested mycelium of the filamentous ascomycete Neocosmospora vasinfecta accumulated C1- against a concentration gradient by a process probably requiring the expenditure of metabolic energy. When mycelium, washed free of growth medium, was incubated in deionized water or tris (hydroxymethyl) aminomethane sulfate at pH 7.5 for 4 h and then transferred to K36C1 solutions, the C1- uptake rate was, on the average, 3.77 +/- 0.26 (+/-SE, N = 20) times the uptake rate exhibited by freshly harvested mycelium. This development of an increased rate of Cl- uptake could be blocked by the presence of an inhibitor of ribonucleic acid synthesis (azaguanine) or of protein synthesis (cycloheximide, fluorophenylalanine, or puromycin). The combined presence of glucose and a potassium salt in the preincubation solution virtually arrested the development of enhanced Cl- uptake. The rate of Cl- uptake by freshly harvested mycelium did not vary greatly with the age of the culture on harvest but the ability to develop an increased rate declined with age. The fact that it is possible to obtain mycelium possessing widely different capacities for Cl- uptake should assist in biochemical characterization of the Cl- uptake system.

Azaguanine↗
PubMed1966

Glucose-C14 metabolism of dormant and activated ascospores of Neurospora.

Budd, Kenneth (The University of Michigan, Ann Arbor), Alfred S. Sussman, and Frederick I. Eilers. Glucose-C(14) metabolism of dormant and activated ascospores of Neurospora. J. Bacteriol. 91:551-561. 1966.-Dormant and activated ascospores of Neurospora tetrasperma, incubated in C(14)-labeled glucose, absorb and metabolize this sugar. At the same time, up to 55% of the CO(2) production from endogenous substrates is quenched, whereas total CO(2) production is unchanged. Glucose-carbon appears in CO(2), lipids, and ethyl alcohol-soluble and -insoluble material in both dormant and activated ascospores, although the proportions entering these fractions differ in the two groups of spores. With few exceptions, the identifiable intermediates of glucose metabolism are the same in dormant and activated ascospores, indicating that the principal pathways may be identical. During glucose metabolism, dormant ascospores accumulate a nondialyzable, ethyl alcohol-soluble polymer, or polymers, which is either absent from activated spores or present in much smaller amounts. This material contains glucose, ribose, and at least nine amino acids, and may represent precursors of more complex cell material which accumulate because of an enzymatic deficiency in the dormant spore. Radioactivity is incorporated into all fractions of the dormant spores and into CO(2) without a noticeable lag, indicating that most, if not all, of the enzymes for glucose utilization are present. A lag in incorporation is observed in the activated spores, which most probably is due to rapid endogenous production of glucose from trehalose, resulting in dilution of lable. After absorption of labeled glucose, two pools of trehalose are found in dormant spores, one of which is extractable without breaking the spores, and the other, only after the spores are disintegrated. The widely differing specific radioactivity of the two pools indicates that these are separated in the intact spore.

Carbon Dioxide↗