Intrinsic effects of solvent polarity on enzymic activation energies

The effect of organic solvents on subtilisin Carlsberg catalysis has been investigated with the aid of a thermodynamic analysis. Saturation solubility experiments were performed to provide a quantitative measure of substrate desolvation from the reaction medium. This enabled calculation of the intrinsic enzymic activation energy and resulted in a linear free energy relationship with respect to solvent polarity. The results indicate that the intrinsic activation energy of subtilisin catalysis is lowest in polar organic solvents, which may be due to transition state stabilization of the enzyme's polar transition state for transesterification.     

The relation of d-alanine and alanine racemase activity in molluscs

• 1.1. Eighteen molluscan species were examined for the presence of d-alanine and alanine racemase activity to probe the probable relation between them.
• 2.2. Two bivalve species had high concentration of d-alanine and l-alanine (1:1) and showed high activities of alanine racemase. In these species, the occurrence of d-alanine could be explained by the action of alanine racemase.
• 3.3. In other species, the levels of d-alanine and enzyme activity were low, and the occurrence of d-alanine did not correspond with the presence of alanine racemase activity.
• 4.4. The mechanism of the occurrence of d-alanine in molluscan tissues seems to vary from species to species and seems not to be associated with the phylogenic situation or habitats of the respective species.

     

The enzymic hydrolysis of amygdalin

Chromatographic examination has shown that the enzymic hydrolysis of amygdalin by an almond beta-glucosidase preparation proceeds consecutively: amygdalin was hydrolysed to prunasin and glucose; prunasin to mandelonitrile and glucose; mandelonitrile to benzaldehyde and hydrocyanic acid. Gentiobiose was not formed during the enzymic hydrolysis. The kinetics of the production of mandelonitrile and hydrocyanic acid from amygdalin by the action of the beta-glucosidase preparation favour the probability that three different enzymes are involved, each specific for one hydrolytic stage, namely, amygdalin lyase, prunasin lyase and hydroxynitrile lyase. Cellulose acetate electrophoresis of the enzyme preparation showed that it contained a number of enzymically active components.     

The enzymic degradation of porphyran

1. The algal galactan, porphyran, was incubated with enzymes from a Cytophaga sp. and the products were examined. 2. Only about 30% of the porphyran was recovered in the form of oligosaccharides, the remainder being of high molecular weight. 3. Among the saccharides were d-galactose, 6-O-methyl-d-galactose, neoagarobiose, neoagarotetraose and oligosaccharides containing 6-O-methyl-d-galactose, the principal of which has been tentatively identified as 6(3)-O-methyl-neoagarotetraose. Fragments containing sulphate were also isolated but not identified. 4. Within the alternating sequence of the d- and l-forms of derivatives of galactose in porphyran, 6-O-methyl-d-galactose replaces d-galactose in a random manner.