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C J Lamb

Publications and source records attributed to C J Lamb.

81 records · Page 5Linked to original sources
PubMed1979

Density labelling studies of the photocontrol of L-phenylalanine ammonia-lyase in discs of potato (Solanum tuberosum) tuber parenchyme.

The photocontrol of L-phenylalanine ammonia-lyase (EC 4.3.1.5) activity in discs of potato (Solanum tuberosum) tuber parenchyme has been investigated by density labelling with 2H from 2H2O. Labelling of enzyme was measured by analysis of the equilibrium distribution of enzyme activity in CsCl density gradients as a function of buoyant density corrected with respect to the distribution of the external marker enzyme beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23). It is demonstrated that the white-light mediated stimulation of phenylalanine ammonia-lyase activity involves stimulation of the rate of de novo production of active enzyme.

Amino Acids↗
PubMed1979

Stimulation of de novo synthesis of L-phenylalanine ammonia-lyase in relation to phytoalexin accumulation in Colletotrichum lindemuthianum elicitor-treated cell suspension cultures of french bean (Phaseolus vulgaris).

(1) The regulation of the accumulation of the isoflavonoid-derived phytoalexin phaseollin in cell suspension cultures of Dwarf French Bean (Phaseolus vulgaris/ has been investigated. (2) An elicitor preparation from cell walls of Colletotrichum lindemuthianum, the causal agent of anthracnose disease of French bean, caused a marked accumulation of phaseollin in the cultures. The elicitor induced phaseollin accumulation to a level of 60% that obtained with the artificial elicitor autoclaved ribonuclease A and was maximally active at a concentration (weight basis) of at least 50 times lower than required for maximal response to ribonuclease. (3) Elicitor preparations from cell walls of Phytophthora megasperma var. sojae, a fungal pathogen of soybean, and Botrytis cinerea, the common grey mould, were much less effective than the C. lindemuthianum wall-released elicitor. (4) There was a marked but transient increase in the extractable activity of phenylalanine ammonia-lyase, the enzyme catalysing the first reaction in the biosynthesis of phaseollin from L-phenylalanine, in response to the elicitor from C. lindemuthianum. (5) Comparative density labelling with 2H from 2H2O indicated that the elicitor stimulates de novo synthesis of phenylalanine ammonie findings provide the basis of a scheme for elicitor induction of phytoalexin accumulation.

Ammonia-Lyases↗
PubMed1979

Synthesis and removal of phenylalanine ammonia-lyase activity in illuminated discs of potato tuber parenchyme.

(1) The synthesis and removal of phenylalanine ammonia-lyase (EC 4.3.1.5) in illuminated discs of potato (Solanum tuberosum cv King Edward) tuber tissue has been investigated by density labelling with deuterium (2H) from deuterium oxide (2H2O) followed by centrifugation to equilibrium in a CsC1 density gradient. (2) Temporal changes in enzyme level have been described in terms of the equation (dE/dt) = ks-kdE where (dE/dt) is the rate of change of enzyme level per unit of tissue (E) with respect to time (t), ks is the rate constant for synthesis of the enzyme and kd is the rate constant for the removal of active enzyme. (3) The optimal concentration of 2H2O was determined by analysis of the relationship between 2H2O concentration, development of enzyme activity and the magnitude of the increase in buoyant density of phenylalanine ammonia-lyase. A concentration of 2H2O of about 40% (v/v) was found to be optimal, allowing achievement of maximal or near maximal increases in the buoyant density of the enzyme without inhibition of the development of enzyme activity, thereby circumventing the major drawback of 2H2O as a source of density label. (4) The overlapping distribution profiles of enzyme activity after density gradient centrifugation were resolved by an iterative method of best fit which allows estimation of the proportions of pre-existing, unlabelled enzyme and newly synthesised, labelled enzyme at the end of the labelling period. This technique has been developed to obtain the rate constants for enzyme synthesis and for removal of active enzyme throughout the period of rapid change in enzyme level. (5) It is demonstrated that the initial rapid increase in phenylalanine ammonia-lyase activity in illuminated discs reflects an increase in the rate constant for enzyme synthesis in the absence of activation of pre-existing enzyme and in the absence of removal of active enzyme. The abrupt transition to a phase of decline in enzyme activity is caused by (a) a reduction in the rate constant for enzyme synthesis and (b) a dramatic increase in the rate constant for removal of active enzyme. The subsequent stabilisation of the enzyme is caused by decay of both rate constants to relatively low levels. (6) The results are consistent with hypothesis that rapid modulation of enzyme levels during tissue differentiation is achieved by simultaneous changesin the rate constants for both enzyme synthesis and for removal of active enzyme.

Ammonia-Lyases↗
PubMed1977

Biophysical and enzymological studies upon the interaction of trans-cinnamic acid with higher plant microsomal cytochromes P-450.

The interaction of trans-cinnamic acid with the cytochrome P-450 of microsomes derived from washed potato slices has been studied. The washing process increased the specific content of microsomal electron transport components and hence provided a useful material in which to study the interaction. Evidence is presented that the trans-cinnamic acid interacts with the cytochrome P-450, and that this interaction is analogous to "type 1" interactions of other cytochrome P-450 systems. This evidence includes the formation of a "type 1" substrate binding spectrum, an increased rate of reduction of cytochrome P-450 by NADPH in the presence of trans-cinnamic acid, an increased oxygen uptake and NADPH oxidation when trans-cinnamic acid is added to the microsomes in the presence of NADPH, and a close correlation between biophysical parameters of electron transport in the cytochrome P-450 system and enzymological parameters of the trans-cinnamic acid 4-hydroxulation reaction. The investigation has been extended to cytochrome P-450 systems of other tissues and it has been found that the trans-cinnamic acid 4-hydroxylation reaction cannot account for the presence of most of th cytochrome P-450 in several tissues. This suggests that other functions of higher plant cytochrome P-450 chains exist, and that the substrate specificityof the hemoprotein may vary in different plant tissues.

Antimycin A↗
PubMed1976

Interpretation of the rate of density labelling of enzymes with 2H2O. Possible implications for the mode of action of phytochrome.

The interpretation of the rate of density labelling of enzymes (the differential or comparative density labelling technique) is considered in terms of two simple models of enzyme turnover. On the basis of this illustrative analysis it is demonstrated that the interpretation of differential (comparative) density labelling experiments is critically dependent on the establishment of a definitive mechanism of enzyme turnover for each particular enzyme studied. In the light of these findings the interpretation of comparative (differential) density labelling experiments appertaining to the mechanism of phytochrome-mediated increases in enzyme activity in higher plants is re-assessed.

Binding Sites↗