PROPERTIES OF A PURIFIED HALOPHILIC MALIC DEHYDROGENASE

Holmes, P. K. (University of Illinois, Urbana), and H. Orin Halvorson. Properties of a purified halophilic malic dehydrogenase. J. Bacteriol. 90:316-326. 1965.-The malic dehydrogenase (MDH) from Halobacterium salinarium required high concentrations of monovalent ions for stability and activity. Studies of inactivation rates at different salt concentrations suggested that approximately 25% NaCl (w/v) is required to stabilize MDH. From 50 to 100% reactivation, depending on the salt concentration present during inactivation, could occur in 2.5 to 5 m NaCl or KCl. The optimal salt concentration for activity of MDH was a function of the pH, and ranged from 1 to 3 m NaCl or KCl. The effect of salt concentration on the pH-activity curves occurred chiefly below pH 7.0. Inactivation of MDH with heat or thiol reagents showed that the enzyme was more labile in the state induced by absence of salt. The activation of MDH by salts was attributed to a decreased rate of dissociation of MDH and reduced nicotinamide adenine dinucleotide (NADH(2)). The inactivation of the enzyme in the absence of salt could be largely prevented by the presence of NADH(2). The S(20.w) of MDH decreased threefold at low salt concentrations. The enzyme was assumed to be in its native compact configuration only in the presence of a high concentration of salt.

BUFFER DISTRIBUTION IN ISOLATED PERFUSED RAT HEART MEASURED BY RUBIDIUM 86

The pattern of distribution of Rb86 in sections of the isolated perfused heart was determined as a measure of uniformity of coronary artery flow. Results suggest that coronary flow was uniform after nonrecirculated perfusion for 15 min. Similar results were obtained in hearts perfused for 30 and for 60 min. The distribution of Rb86 was comparable in hearts perfused for 30 min with perfusate circulated through either coarse porosity, sintered-glass filters or 5-µ Millipore filters. A nonuniform distribution of isotope was demonstrated with ligation of branches of coronary arteries and with the introduction of air. The results suggest that hearts perfused by recirculation of buffer through coarse porosity, sintered-glass filters have a uniform distribution of perfusate throughout the heart.

PROTEIN-PROTEIN INTERACTIONS AMONG L POLYPEPTIDE CHAINS OF BENCE-JONES PROTEINS AND HUMAN GAMMA-GLOBULINS

The L polypeptide chains of certain Bence-Jones proteins of group I have been found in three forms: monomers of molecular weight of about 20,000, dimers which monomerize in dissociating solvents, and dimers which are stable in such solvents. The L polypeptide chains of some Bence-Jones proteins of group II were found to occur naturally only as stable dimers. The L chains of normal human γ-globulin have been obtained in a reduced unalkylated form, and a fraction of these chains was found to form stable dimers under oxidizing conditions. It is suggested that a single disulfide bond is involved in stabilization of the dimer. In experiments on the reconstitution of 7S γ-globulin, it was found that stable dimers of L polypeptide chains did not associate appreciably with H_γ chains to form a soluble product. L chains in the monomeric form, both of a reduced alkylated Bence-Jones protein and of reduced unalkylated γ-globulin, combined with H_γ chains to form a 7S product. After hydrolysis with papain, the 7S material containing the Bence-Jones L chains yielded fragments comparable to the fragments of papain-treated myeloma proteins. As indicated by spectrofluorometric measurements, dissociable dimers and stable dimers of the L chains of a Bence-Jones protein both underwent identical thermally induced transitions in the temperature range 48–58°C. When L polypeptide chains were present in reduced alkylated γ-globulin or reduced alkylated S fragments, no transition occurred until 65°C, the coagulation temperature of γ-globulin and S fragments. Above this temperature, L chains were released into solution. These experiments suggested that free L chains and L chains bound to H_γ chains have different conformational stabilities.

ENZYMATIC DEACYLATION OF S35-BENZYLPENICILLIN

Pruess, David L. (University of Wisconsin, Madison), and Marvin J. Johnson. Enzymatic deacylation of S(35)-benzylpenicillin. J. Bacteriol. 90:380-383. 1965.-S(35)-benzylpenicillin, penicilloic acid, and penilloic acid were deacylated by cell suspensions of Escherichia coli and Micrococcus roseus. Both cultures deacylated penicillin most rapidly and penilloic acid least rapidly. The deacylase activity of M. roseus against penicilloic acid was cell-bound, probably requiring a metal ion for activity.

BLOOD-FREE MEDIUM FOR THE RAPID GROWTH OF PASTEURELLA TULARENSIS

A medium composed of (in g/100 ml) Tryptose broth with thiamine (Difco), 2.6; cysteine-HCl, 0.12; glucose, 1; FeSO(4), 7H(2)O, 0.005; KCl, 0.02; histidine, 0.1; tris(hydroxymethyl)aminomethane (tris) buffer, 0.3; and agar, 1; will support rapid growth of the fully virulent SCHU-S4 strain of Pasteurella tularensis. Although the test organism grew rapidly on medium from which KCl and tris buffer were omitted, these two components increased the stability of the medium upon storage at 4 C. It was necessary to (i) control carefully the relative concentration of the ferrous iron and cysteine-HCl, (ii) incubate the prepared medium overnight prior to use, and (iii) incubate the inoculated plates in an atmosphere of high relative humidity. Rapid growth of the organism was obtained also from very small inocula in the liquid form of the medium. Biochemical studies designed to elucidate the mechanisms involved in the enhancement of growth of P. tularensis in this relatively simple blood-free medium were initiated.

RED CELL ACID PHOSPHATASE: RACIAL DISTRIBUTION AND REPORT OF A NEW PHENOTYPE

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