Enzyme catalysis in microgravity: an intricate problem to be solved.
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Catalysis↗
Biomedical subjects
F Ranaldi
Publications and source records attributed to F Ranaldi.
Multisite inhibition of Pinus pinea isocitrate lyase by phosphate.
Our results show that the phosphate ion is a nonlinear competitive inhibitor of Pinus pinea isocitrate lyase. In addition, this compound induces a sigmoidal response of the enzyme, which usually exhibits standard Michaelis-Menten kinetics. This peculiar behavior of P. pinea isocitrate lyase could be explained by a dimer (two-site) model, in which phosphate binds cooperatively, but the affinity of the vacant site for substrate (the magnesium-isocitrate complex) remains the same. As a result, the interaction of phosphate with free enzyme produces an inhibitor-enzyme-inhibitor species that is of significant importance in determining reaction rate; a possible regulatory role of the glyoxylate cycle by inorganic phosphate is suggested. The mode of phosphate inhibition is consistent with both the mechanism for magnesium ion activation of P. pinea isocitrate lyase and its site heterogeneity. Our results explain the cooperative effects observed by some authors in kinetic studies of isocitrate lyase carried out in phosphate buffers and also account for the higher K(m) values determined by using such assay systems. Phosphate buffer should be avoided in performing isocitrate lyase kinetics.
Buffers↗
Enzyme kinetic parameters are not altered by microgravity.
This paper deals with a microgravity experiment concerning the EMEC project (Effect of Microgravity on Enzymatic Catalysis), performed during the parabolic flight of the sounding rocket MASER 7, launched from the base of Esrange (Kiruna, Sweden) on May 3, 1996. The experiment consisted of performing, in a microgravity environment, a number of velocity measurements of an enzyme (isocitrate lyase) catalyzed reaction at different substrate concentrations, to calculate the kinetic parameters (Km and Vmax), which were compared with those obtained at standard gravity, with identical instrumentation. The experimental hardware, the EMEC module, expressly set up by Officine Galileo (Firenze, Italy) with the financial support of the European Space Agency, was a multichannel fibre-optics radiometer, equipped with an automatic injection system, that allowed to measure simultaneously the transmittance changes in 16 reaction cells. The results indicated that under the experimental conditions applied, microgravity has no appreciable effect on the enzyme kinetic constants.
Catalysis↗
[Activity of glyoxylate cycle during the culture of Rhodotorula gracilis in the presence of fatty acids and detergents].
In this work on Rhodotorula gracilis, we studied the level of the representative enzymes of foundamental metabolic ways (HK, PK, G6PDH and IDH) and those of ICL and MS key enzymes of glyoxylate cycle with different carbone sources. The glucose appears the best source of carbone for all the tested enzymes except ICL and MS which are practically absent in the cells developed with this carbone source. In presence of acetate and ethanol we have obtained the expression of the glyoxylate cycle enzymes (ICL and MS). Moreover we obtained the operativity of the glyoxylate cycle in the lipid-rich cells or cells developped on neutral detergents or anionics similar to the fatty acids.
Detergents↗
[Lactate as competitive inhibitor of Pinus pinea isocitrate lyase].
We studied the effect of L-lactate on both the cleavage and the condensation reactions of Pinus pinea isocitrate lyase. This compound is a competitive of Pinus pinea isocitrate lyase towards both isocitrate and glyoxylate, whereas is a mixed type inhibitor towards succinate. Assuming that L-lactate acts as a glyoxylate analogue, our finding agrees with an uni-bi ordered mechanism of isocitrate lyase, with glyoxylate first substrate to enter the active site in the condensation reaction. Results are discussed and compared with those known in the literature about other structurally related metabolites.
Binding, Competitive↗
Study of second messenger levels and of sugar catabolism enzyme activities in transformed cells resistant to ionizing radiations.
We measured the level of second messengers, the activity of carbohydrate metabolism enzymes, and the resistance to ionizing radiations in normal 32D hematopoietic cells, in v-erbB transformants and in spontaneous transformants. v-erbB and spontaneous transformants were resistant to radiations as compared with their normal counterpart. The second messenger diacylglycerol was elevated in radioresistant clones. Only v-erbB transformants showed increase of the activities of enolase and glucose-6-phosphate dehydrogenase. v-erbB-transformed NIH/3T3 cells, selected as control, showed identical correlation between radioresistance, increase of diacylglycerol, and of enolase and glucose-6-phosphate dehydrogenase activity. These results indicate that increase of diacylglycerol is correlated with resistance to the killing effect of ionizing radiations and could be proposed as a marker of radioresponse.
3T3 Cells↗
A review of human cervical mucus enzymes.
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Animals↗
Is the salivary "ferning" a reliable index of the fertile period?
We found that the fern leaf crystallisation of human saliva is a non-specific phenomenon, independent on the action of estrogenic hormones. Salivary ferning can be obtained in practice during the whole menstrual cycle and occurs in the saliva of postclimateric, pregnant and prepuberal women. Even the saliva of male subjects gives invariably the ferning reaction. In conclusion, salivary ferning does not seem a reliable method to establish woman fertile period.
Crystallization↗