Biomedical subjects
Publications and source records attributed to P J Syrett.
Uptake of nitrate and urea by Phaeodactylum tricornutum is shown to be a sodium dependent process inhibited by lithium or potassium. The half-saturation constant for sodium (KNa) was 2.6 mM for nitrate uptake and 71 mM for urea uptake. It is suggested that sodium dependent uptake mechanisms may be characteristic of marine plants.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
1. When acetate-adapted cells of Chlorella are suspended in nitrogen-free medium and supplied with glucose, isocitrate lyase activity disappears from the cells at a rate of about 9%/h. This loss of activity is shown to be accompanied by loss of isocitrate lyase protein. 2. When isocitrate lyase activity is assayed in intact cells after freezing and thawing, the rate of loss of activity after addition of glucose approaches 20%/h. 3. It is shown, by using (35)S, that the rate of turnover of isocitrate lyase protein is somewhat lower than that of other major soluble proteins; general protein turnover during nitrogen starvation, and after glucose addition, is too slow to account for the rate of loss of isocitrate lyase protein. 4. Disappearance of isocitrate lyase activity must result from a mechanism that allows degradation of this specific protein under conditions of limiting nitrogen supply.
Explore the source record for details and available documents.
1. Intermediary metabolites, arising from the glyoxylate by-pass, were tested for their effect on the activity of isocitrate lyase, the first enzyme of the by-pass. 2. Oxaloacetate and pyruvate inhibited the enzyme when present at concentrations similar to that of the substrate. 3. Inhibition was competitive and did not depend on a non-optimum pH. The affinities determined at the pH optimum were: K(i) (oxaloacetate), 3.7x10(-5)m; K(i) (pyruvate), 6.6x10(-5)m. 4. The significance of the inhibitions is discussed with particular reference to the known inhibition by phosphoenolpyruvate.
1. Isocitrate lyase (threo-d(s)-isocitrate glyoxylate-lyase, EC 4.1.3.1) has been purified from acetate-adapted cells of Chlorella pyrenoidosa. 2. The final preparation was homogeneous by the criteria of sedimentation, diffusion and polyacrylamide-gel electrophoresis. 3. The sedimentation coefficient (S(20,w)) was 9.04x10(-13)sec. and the diffusion coefficient (D(20,w)) 4.62x10(-7)cm.(2)/sec.; from these values the molecular weight of the enzyme was calculated to be 170000 and its Stokes radius to be 4.63x10(-7)cm. 4. The elution of the enzyme from Sephadex G-100 was studied and estimates of molecular weight and Stokes radius were obtained from the elution data. 5. The turnover number of the enzyme was 5950moles of glyoxylate formed/min./mole of enzyme at 30 degrees . 6. With threo-d(s)(+)-isocitrate as substrate, the K(m) of the enzyme was 0.023mm.
1. Thiobacillus strain C oxidized [(35)S]thiosulphate completely to sulphate. 2. During thiosulphate oxidation [(35)S]sulphate was formed more rapidly from (S.(35)SO(3))(2-) than from ((35)S.SO(3))(2-). (35)S disappeared less rapidly from thiosulphate with ((35)S.SO(3))(2-) as substrate than with (S.(35)SO(3))(2-). 3. Thiosulphate labelled in both atoms was produced during ((35)S.SO(3))(2-) oxidation, but not during (S.(35)SO(3))(2-) oxidation. 4. No (35)S was precipitated as elementary sulphur either in the presence or absence of exogenous unlabelled sulphur. 5. During [(35)S]thiosulphate oxidation, appreciable quantities of [(35)S]trithionate accumulated and later disappeared. Other polythionates did not accumulate consistently. 6. [(35)S]Trithionate was formed initially at a greater rate from (S.(35)SO(3))(2-) than from ((35)S.SO(3))(2-), but subsequently at a similar rate from each. 7. Trithionate formed from (S.(35)SO(3))(2-) was labelled only in the oxidized sulphur atoms, but that formed from ((35)S.SO(3))(2-) was labelled in both oxidized and reduced atoms. The proportion of (35)S in the oxidized atoms increased as more trithionate accumulated. 8. The results eliminate some mechanisms of trithionate formation but are consistent both with a mechanism of thiosulphate oxidation based on an initial reductive cleavage of the molecule and with a mechanism in which thiosulphate undergoes an initial oxidative reaction.
Explore the source record for details and available documents.