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M A Hooks

Publications and source records attributed to M A Hooks.

22 records · Page 2Linked to original sources
PubMed1989

Compartmentation of Nucleotides in Corn Root Tips Studied by P-NMR and HPLC.

Corn (Zea mays L.) root tips were subjected to different conditions so that nucleotide levels varied over a wide range. Levels of nucleotides in corn root tips were measured using (31)P nuclear magnetic resonance (NMR) spectroscopy and high performance liquid chromatography. Results indicate: (a) Similar amounts of NTP and sugar nucleotides were observed by in vivo NMR and in extracts. In contrast, a significant amount of NDP observed in root tip extracts was not detected by in vivo NMR. Thus, for a given sample, [NTP]/[NDP] ratios determined in vivo by (31)P-NMR are always higher than ratios observed in extracts, deviating by approximately 4-fold at the highest ratios. The NMR-invisible pool of NDP appeared quite metabolically inert, barely changing in size as total cell NDP changed. We conclude that NDP in corn root tips is compartmented with respect to NMR visibility, and that it is the NMR-visible pool which responds dynamically to metabolic state. The NMR-invisible NDP could either be immobilized (and so have broad, undetectable NMR signals), or be complexed with species that cause the chemical shift of NDP to change (so it does not contribute to the NMR signal of free NDP), or both. (b) (31)P-NMR cannot distinguish between bases (A, U, C, and G) of nucleotides. HPLC analysis of root tip extracts showed that the relative amount of each base in the NTP and NDP pools was quite constant in the different samples. (c) In extracts, for each of the nonadenylate nucleotides, [NTP]/[NDP] was linearly proportional to [ATP]/[ADP], indicating near equilibrium in the nucleoside diphosphokinase (NDPK) reaction. However, the apparent equilibrium constants for the phosphorylation of GDP and UDP by ATP were significantly lower than 1, the true equilibrium constant for the NDPK reaction. Thus, for a given sample, [ATP]/[ADP] approximately [CTP]/[CDP] > [UTP]/[UDP] > [GTP]/[GDP]. This result suggests that the different NDPs in corn root tips do not have equal access to NDPK.

Journal Article↗
PubMed1986

Recovery of phenytoin from an enteral nutrient formula.

The recovery of phenytoin from phenytoin oral suspension dispersed in an enteral nutrient formula was determined. The study was conducted in two phases. In phase 1, diluted phenytoin oral suspension was added to 10 1-mL samples of full-strength Osmolite and 10 1-mL samples of a distilled water control solution to produce a theoretical concentration of 10 micrograms/mL. The samples were filtered through an ultrafiltration membrane and assayed for phenytoin concentration by a homogeneous enzyme-multiplied immunoassay technique. In phase 2, varying amounts of diluted phenytoin oral suspension were added to 30-mL quantities of half-strength Osmolite or control solution to determine the effect of phenytoin concentration on recovery of phenytoin; also, a constant amount of diluted phenytoin oral suspension was added to 30-, 60-, and 90-mL quantities of half-strength Osmolite or control solution to determine the effect of solvent volume on recovery of phenytoin. Duplicate samples of each phase 2 mixture were filtered and assayed in the same manner as phase 1 samples. The mean concentration of phenytoin in phase 1 samples was 3.70 +/- 0.28 microgram/mL for Osmolite and 9.87 +/- 0.27 microgram/mL for control solution; this difference was significant. The percentage of phenytoin recovered from phase 2 samples of Osmolite increased with increasing phenytoin concentration and decreased with increasing volumes of Osmolite. The decreased recovery of phenytoin from the enteral nutrient formula used in this study has potential clinical importance, but further research in humans is needed to substantiate these in vitro observations.

Enteral Nutrition↗