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Biomedical subjects

D B Dickinson

Publications and source records attributed to D B Dickinson.

At least 37 records · Page 2Linked to original sources
PubMed1973

Partial Characterization of C(x) Cellulase and Cellobiase from Ripening Tomato Fruits.

Cellulolytic enzymes were studied in extracts from the locular contents of ripening fruits of Lycopersicon esculentum var. KC-146. When acting on carboxymethyl cellulose, the enzyme preparations were capable of decreasing the viscosity of the reaction mixture and generating reducing groups, oligosaccharides, and glucose. Cellobiose cellotriose, cellotetrose, and cellopentose also served as substrates for glucose production.These properties were due to the presence in the extracts of two cellulolytic enzymes-C(x) cellulase (E.C. 3.2.1.4) and cellobiase- (E.C. 3.2.1.21). No evidence was found for the presence of exocellulase or C(1), an enzyme which initiates enzymatic attack on insoluble cellulose.Cellobiose was found to be weakly inhibitory to C(x) cellulase. d-Glucono-1,5-lactone competitively inhibited cellobiase. The K(m) for cellobiose was 0.34 mm, and the K(i) for gluconolactone was 23 muM.

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PubMed1973

Hexokinase from maize endosperm and scutellum.

Hexokinase (EC 2.7.1.1) was isolated from endosperm and scutellum of developing and germinating maize (Zea mays) seeds. With fructose as the variable substate, Michaelis constant values for the scutellum enzyme were about onethird those of the endosperm enzyme (0.05 versus 0.15 mm), and no developmental differences were observed. With glucose as the variable substrate, Michaelis constant values were all in the range 0.1 to 0.2 mm. The enzyme preparation from germinating scutellum was studied further; when glucose was varied over a wide range, a Michaelis constant of 3.4 mm was observed in addition to the much lower Michaelis constant noted above. This low affinity binding of glucose may have regulatory significance and may indicate the presence of a glucokinase in addition to hexokinase.

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PubMed1973

Some Physiological Effects of Viviparous Genes vp(1) and vp(5) on Developing Maize Kernels.

The effects of two viviparous genes, vp(1) and vp(5), on development of the maize (Zea mays L.) embryo and endosperm were investigated. Differences between viviparous and normal embryos first appeared at 25 to 30 days after pollination. Increases in fresh weights indicated that viviparous began to grow more rapidly than normal embryos at that time. Amino acids and ethanol-soluble carbohydrates also accumulated more rapidly in viviparous, but a reserve material (lipid) was lower in viviparous than in normal embryos.The fresh and dry weights and total nitrogen content of endosperms from viviparous resembled those of normal seeds until about 30 days after pollination, but were all lower in viviparous after that time. Pronounced differences in alpha-amylase activity were not observed until late in development (40 days after pollination) when the enzyme increased in viviparous seeds only. Developmental changes in viviparous seeds generally resemble those of normally germinating seeds.

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PubMed1970

Freezing damage to isolated tomato fruit mitochondria as modified by cryoprotective agents and storage temperature.

Isolated tomato (Lycopersicon esculentum var. Kc 146) fruit mitochondria could be stored successfully in the frozen state without a cryoprotective agent if the mitochondria were frozen quickly by immersion in liquid nitrogen and later thawed quickly at 30 C. Criteria of freezing damage were rate of respiration, adenosine diphosphate to oxygen ratio, and respiratory control ratio. Marked reduction in respiration and loss of respiratory control occurred when mitochondria were transferred from liquid nitrogen to -5, -10, or -18 C for 15 minutes prior to thawing at 30 C. Dimethylsulfoxide (5%) prevented freezing damage when mitochondria were incubated at -5 C but did not prevent freezing damage at -10 or -18 C. Isolated tomato mitochondria show promise as a model system for studying the nature of freezing damage and the mode of action of cryo-protective agents.

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PubMed1969

Presence of ADP-Glucose Pyrophosphorylase in Shrunken-2 and Brittle-2 Mutants of Maize Endosperm.

ADP-Glucose pyrophosphorylase activity has been detected in relatively low amounts in the embryos and endosperms of sh(2) and bt(2) mutant maize seeds. The total enzyme activities in sh(2) and bt(2) were about 12% and 17% respectively, of that found in starchy maize seeds (Dekalb 805). The ADP-glucose pyrophosphorylases from the starchy and mutant maize seeds were activated by 3-phosphoglycerate. However, the extent of the activation of the sh(2) enzyme was not as great as that observed with the bt(2) and Dekalb 805 enzymes. The low levels of ADP-glucose pyrophosphorylase activity in the maize mutants correlate well with the low levels of starch found in the endosperm of these mutants.

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PubMed1968

Rapid starch synthesis associated with increased respiration in germinating lily pollen.

In vitro studies of germinating Lilium longiflorum pollen showed that starch increased more rapidly during the first 30 minutes of incubation than during the next several hours. The period of rapid starch formation coincided with the first period of high respiration. An estimate was made of the extra ATP utilized to form extra starch during the first 30 minutes, and this estimate indicates that starch synthesis accounts for a significant portion of the initial high rate of respiration. This pattern of respiration and starch synthesis was not altered when pollen germinated in a pentaerythritol medium that could not be metabolized instead of the standard sucrose medium.Sucrose was the predominant sugar in mature lily pollen. This sugar decreased 50% during several hours incubation in pentaerythritol culture medium. Reducing sugars remained low during incubation which may indicate that sucrose breakdown is regulated by the rate of utilization of hexose units.

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PubMed1968

Dimethyl sulfoxide: reversible inhibitor of pollen tube growth.

Five percent dimethyl sulfoxide (DMSO) completely inhibited tube initiation, stopped tube growth and suppressed the high respiration associated with tube growth of lily pollen. The effect of DMSO on respiration was indirect because uncoupling concentrations of 2,4-dinitrophenol abolished the inhibition of respiration. Five percent DMSO did not inhibit rapid starch synthesis during the first 30 minutes of incubation, nor did DMSO inhibit the period of high respiration associated with rapid starch synthesis. DMSO did not cause permanent damage to the cells since normal pollen tube growth occurred after its removal. Dimethyl sulfoxide is not a general inhibitor of pollen metabolism, but it may be a specific inhibitor of a process required for tube growth.

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