SOLVOLYSIS OF ORGANIC PHOSPHATES. VII. SPONTANEOUS HYDROLYSIS OF 2,2,2-TRICHLOROETHYL PHOSPHATE

1972 ◽  
Vol 1 (8) ◽  
pp. 699-702 ◽  
Author(s):  
Yukito Murakami ◽  
Junzo Sunamoto ◽  
Naomi Kanamoto
Keyword(s):  
Organic Phosphates ◽  
Spontaneous Hydrolysis ◽  
Hydrolysis Of

Phosphorus compounds measured in a rapid and simple leaf test for the assessment of the phosphorus status of subterranean clover

1984 ◽  
Vol 24 (125) ◽  
pp. 213 ◽  
Author(s):  
GCJ Irving ◽  
D Bouma
Keyword(s):  
Leaf Tissue ◽  
Rapid Test ◽  
Subterranean Clover ◽  
Exchange Chromatography ◽  
Phosphorus Compounds ◽  
Fresh Leaf ◽  
Organic Phosphates ◽  
Phosphorus Status ◽  
Colour Development ◽  
Hydrolysis Of

Experiments were done to determine what proportion of the phosphate extracted from fresh leaf tissue by five drops of 10 N H2SO4 represents inorganic tissue phosphate, and to what extent hydrolysis of organic phosphates during and after the extraction, and during the development of the blue phosphomolybdate complex, could contribute to the values obtained. The extraction is the basis of a simple and rapid test for the assessment of the phosphorus status of subterranean clover (Bouma and Dowling 1982). Extraction of leaf tissue of subterranean clover and sunflower with 0.2 M HClO4 at O�C, which was shown to extract inorganic leaf phosphorus without causing significant hydrolysis of organic phosphates, gave values not significantly different from those in H2SO4 extracts. The rate of hydrolysis of endogenous organic phosphates in tissue, extracted and left at room temperature for periods of up to 40 min. after adding H2SO4, did not differ significantly from zero. Errors due to hydrolysis during the 30 min. previously recommended for colour development are reduced to negligible proportions by reducing the time for colour development to 10 min. and by adding citric acid at this point. Anion-exchange chromatography of 10 N H2SO4 and 0.2 M HClO4 extracts confirmed the similarity of their composition and provided estimates of the various phosphate compounds present. The extraction of fresh leaf tissue with 10 N H2SO4 provides a satisfactory estimate of the endogenous inorganic phosphorus content.

THE ACETYLATION OF THROMBIN

1959 ◽  
Vol 37 (1) ◽  
pp. 1361-1366 ◽  
Author(s):  
Ricardo H. Landaburu ◽  
Walter H. Seegers
Keyword(s):  
Methyl Ester ◽  
Proteolytic Activity ◽  
Basic Structure ◽  
Amino Groups ◽  
Spontaneous Hydrolysis ◽  
Optimum Ph ◽  
Hydrolysis Of

Purified thrombin-C loses its clotting power upon acetylation. The thrombin-E which is produced during the acetylation has approximately twice the proteolytic activity as the original thrombin-C. Evidently amino groups are not necessary to have thrombin-E activity, but if o-acyl groups are also produced the enzyme does not hydrolyze p-toluenesulphonylarginine methyl ester (TAMe). The activity can be recovered by spontaneous hydrolysis of the o-acyl groups at pH 8.5. Thrombin-E does not activate fibrinogen, but does lyse fibrin. The optimum pH with TAMe as substrate is 8.8. It may be that thrombin-C is a dimer of the basic structure in thrombin-E.

Spontaneous Hydrolysis of Glycosides

1998 ◽  
Vol 120 (27) ◽  
pp. 6814-6815 ◽  
Author(s):  
Richard Wolfenden ◽  
Xiangdong Lu ◽  
Gregory Young
Keyword(s):  
Spontaneous Hydrolysis ◽  
Hydrolysis Of

scholarly journals Common-type acylphosphatase: steady-state kinetics and leaving-group dependence

1997 ◽  
Vol 327 (1) ◽  
pp. 177-184 ◽  
Author(s):  
Paolo PAOLI ◽  
Paolo CIRRI ◽  
Lucia CAMICI ◽  
Giampaolo MANAO ◽  
Gianni CAPPUGI ◽  
...  
Keyword(s):  
Inorganic Phosphate ◽  
Strong Dependence ◽  
Common Type ◽  
Enzyme Active Site ◽  
Enzyme Substrate ◽  
Linear Relationships ◽  
Steady State Kinetics ◽  
Spontaneous Hydrolysis ◽  
Leaving Group ◽  
Hydrolysis Of

A number of acyl phosphates differing in the structure of the acyl moiety (as well as in the leaving-group pKa of the acids produced in hydrolysis) have been synthesized. The Km and Vmax values for the bovine common-type acylphosphatase isoenzyme have been measured at 25 °C and pH 5.3. The values of kcat differ widely in relation to the different structures of the tested acyl phosphates: linear relationships between log kcat and the leaving group pKa, as well as between log kcat/Km and the leaving-group pKa, were observed. On the other hand, the Km values of the different substrates are very close to each other, suggesting that the phosphate moiety of the substrate is the main chemical group interacting with the enzyme active site in the formation of the enzyme–substrate Michaelis complex. The enzyme does not catalyse transphosphorylation between substrate and concentrated nucleophilic acceptors (glycerol and methanol); nor does it catalyse H218O–inorganic phosphate oxygen exchange. It seems that no phosphoenzyme intermediate is formed in the catalytic pathway. Furthermore, during the enzymic hydrolysis of benzoyl phosphate in the presence of 18O-labelled water, only inorganic phosphate (and not benzoate) incorporates 18O, suggesting that no acyl enzyme is formed transiently. All these findings, as well as the strong dependence of kcat upon the leaving group pKa, suggest that neither a nucleophilic enzyme group nor general acid catalysis are involved in the catalytic pathway. The enzyme is competitively inhibited by Pi, but it is not inhibited by the carboxylate ions produced during substrate hydrolysis, suggesting that the last step of the catalytic process is the release of Pi. The activation energy values for the catalysed and spontaneous hydrolysis of benzoyl phosphate have been determined.

Sign in / Sign up

Export Citation Format

Share Document