J. Tze-Fei Wong

A novel criterion for enzymic mechanisms involving three substrates

Abstract For differentiation between linear mechanisms for enzymic reactions involving three substrates, the use of a new criterion has been examined. It evolves from the fact that in many such mechanisms various potential terms in the denominator of the rate equation can have finite values only if one or more reaction products are added to the system. Thus the criterion is said to be based on the recall of absent terms by addition of reaction products. The recall patterns for a range of model mechanisms have been analyzed.

Purification of isoacceptor transfer RNA by affinity coupling to aldehyde-containing matrix

A method has been developed for the affinity coupling of aminoacyl-tRNA to an aldehyde-containing polymer by means of reduction with sodium cyanoborohydride. Sephadex dialdehyde obtained from periodate oxidation of Sephadex G-50, and Enzacryl polyaldehyde obtained from hydrolysis of Enzacryl polyacetal, were found to provide the requisite polymeric matrix. This coupling reaction permitted the rapid purification of isoacceptor tRNAs of Escherichia coli for the alpha-amino acids glycine, valine, and arginine, as well as the alpha-imino acid proline.

Initial studies of hypoxic radioprotection by deoxygenated dextran-hemoglobin

Initial studies were performed to examine the potential of perfused dextran-hemoglobin to protect pig skin or mouse bone marrow cells against radiation damage. Some protection was indicated in both systems. In the pig skin a protection factor of 1.5 was observed for moist desquamation, and 2.0 for necrosis. These results suggest the possibility of using blood substitutes to induce tissue hypoxia for therapeutic purposes.

Ligand binding to protein measured by gel filtration on a dispersion column.

A double conical gel-permeation column is described, which permits an efficient dispersion of solutes in passage. It makes possible a facile determination of ligand binding to protein on the basis of the differential gel permeation of these molecules. The system has been applied, using Sephadex G-25 beads as column packing, to measure [3H]tryptophan binding to bovine serum albumin.

Biophysical basis of hypoxic radioprotection by deoxygenated dextran-hemoglobin☆

Perfusion with deoxygenated dextran-hemoglobin provides an effective method for inducing hypoxic radioprotection of normal tissues during radiation treatment of tumors. In this study, the dependence of P50, the half-saturation pressure of oxygen binding to dextran-hemoglobin, was analyzed as a function of solution temperature and pH. The variation of attainable radioprotection with P50, and with the amount of collateral blood entering into the perfused region, was calculated. Upon perfusion of canine gracilis muscle with deoxygenated dextran-hemoglobin, a rapid onset of extensive venous hypoxia was observed.

The mechanism of liver alcohol dehydrogenase

Abstract After repeated treatments with charcoal, the capacity of liver alcohol dehydrogenase to catalyze an exchange reaction between ethanol an acetaldehyde was, within limits of analysis, totally dependent on the addition of nicotinamide adenine dinucleotide coenzyme. This observation ruled out the free existence of oxidized and reduced forms of the enzyme in the enzymic mechanism, and its quantitative implication on the possibility of a cyclic oxidation and reduction of the enzyme during catalysis is discussed.

A novel synthesis of 3,5-diiodotyrosine with iodic acid

Based on Landolts reaction between iodic acid and sulfite to produce iodine, a method has been developed for the high-yield iodination of tyrosine to form diiodotyrosine without significant formation of monoiodotyrosine. The use of sulfite as reductant for iodic acid cannot be effectively replaced by citric or oxalic acid under the reaction conditions.

Complementary base-pairing properties of cyclized and linear oligonucleotides

Oligouridylates of varying chain lengths were synthesized by polynucleotide phosphorylase and cyclized by RNA ligase. Over chain lengths from 7 to 15, the bindings of the cyclized and linear oligomers to polyadenylate were measured on the basis of differential migration of bound and free oligomers on a gel exclusion column. Binding of the cyclized oligomers was found to be far weaker than that of their linear counterparts of equal length. Such a general reduction in base-pairing capacity due to the cyclized conformation, by limiting the strength of unintended base-pairing without obstructing the possible development of strong specific base-pairing, may represent an advantage important to the function and evolution of loop structures in tRNA and other RNA molecules.