Subuni ts . . . . . . . . . . . . . . . . . . . . . . 250 Number . . . . . . . . . . . . . . . . . . . . . 250 Molecular weight and s to ich iomet ry . . . . . . . . . . . . . 251 Isola t ion and amino acid compos i t ion . . . . . . . . . . . . 252 Impuri t ies or products o f proteolysis . . . . . . . . . . . . . 255 Biogenesis . . . . . . . . . . . . . . . . . . . . 255 Comparison wi th other ATPases . . . . . . . . . . . . . . 256

Mitochondrial adenosine triphosphatase

The branched-chain amino acids are synthesized by plants, fungi and microorganisms, but not by animals. Therefore, the enzymes of this pathway are potential target sites for the development of antifungal agents, antimicrobials and herbicides. Most research has focused upon the first enzyme in this biosynthetic pathway, acetohydroxyacid synthase (AHAS) largely because it is the target site for many commercial herbicides. In this review we provide a brief overview of the important properties of each enzyme within the pathway and a detailed summary of the most recent AHAS research, against the perspective of work that has been carried out over the past 50 years.

Acetohydroxyacid synthase and its role in the biosynthetic pathway for branched-chain amino acids

A highly stable adenosine triphosphatase from a thermophillie bacterium. Purification, properties, and reconstitution.

INTRODUCTION .......... ....................................... 320 THE THERMOPHILIC MICROORGANISMS .......... ......................... 321 POSSIBLE MECHANISMS OF SURVIVAL .......... .......................... 322 Lipids ................................................. 322 Rapid Resynthesis ............ ..................................... 322 Thermally Stable Macromolecules .............................................. 323 PROTEINS FROM THERMOPHILIC MICROORGANISMS ..... ............... 323 Classification ........ ......................................... 323 Red Fraction .. ............................................... 324 Adenosine Triphosphatase .................................................. 324 Flagella ................................................. 325 Amylase ................................................. 325 Aldolase ................................................. 329 Proteolytic Enzymes .............. ................................... 330 Dehydrogenases .......... ....................................... 331 Ferredoxin ................................................. 332 Formyltetrahydrofolate Synthetase ............................................. 333 fl-Galactosidase .......... ....................................... 333 Phosphoglucomutase ................................................. 333 Glucose-6-Phosphate Isomerase ................................................. 333 Enolase ................................................. 334 ALLOSTERIC INTERACTIONS ................................................. 334 Aspartokinase ......... ........................................ 334 Threonine Deaminase ................................................. 334 Phosphofructokinase ................................................. 334 Fructose-1, 6-Diphosphatase ................................................. 335 CONCLUSIONS, SPECULATIONS, AND SUMMARY ...... ................... 335 LITERATURE CITED ................................................. 338

Proteins from thermophilic microorganisms.

(1) Extensive studies on proton-translocating ATPase (H+-ATPase) revealed that H+-ATPase is an energy transforming device universally distributed in membranes of almost all kinds of cells. (2) Crystallization of the catalytic portion (F1) of H+-ATPase showed that F1 is a hexagonal molecule with a central hole. The diameter of F1 is about 90 A and its molecular weight is about 380,000. (3) Use of thermophilic F1 permits the complete reconstitution of F1 from its five subunits (α, β, γ, δ, and e) and demonstration of the gate function of the γδe-complex, the catalytic function of β (supported by α and γ), and the H+-translocating functions of all five subunits. (4) Studies using purified thermostable F0 showed that F0 is an H+-channel portion of H+-ATPase. The direct measurement of H+-flux through F0, sequencing of DCCD-binding protein, and isolation of F1-binding protein are described. (5) The subunit stoichiometry of F1 may be α3β3γδe. (6) Reconstitution of stable H+-ATPase-liposomes revealed that ATP is directly synthesized by the flow of H+ driven by an electrochemical potential gradient and that H+ is translocated by ATP hydrolysis. This rules out functions for all the hypothetical components that do not belong to H+-ATPase in H+-driven ATP synthesis. The roles of conformation change and other phenomena in ATP synthesis are also discussed.

Structure and function of H + -ATPase

Studies on an ATPase of thermophilic bacteria. I. Purification and properties.

Threonine deaminase [EC 4.2.1.16] was highly purified from Bacillus stearothermophilus. The enzyme exhibited maximum activity at 65 degrees and at pH 9.2--9.6. It was inactivated on dilution and on storage at 4 degrees, but was protected by egg albumin. The enzyme was labile at 65 degrees, but became stable in the presence of egg albumin and isoleucine at pH 7.0. The substrate saturation curve for the enzyme reaction at 40 or 65 degrees was hyperbolic, but in the presence of isoleucine, the curve became sigmoidal (n = 2). The enzyme was more sensitive to isoleucine at 40 degrees than at 65 degrees, while valine slightly inhibited the enzyme at both 40 and 65 degrees. Inhibition of the enzyme by isoleucine was antagonized by valine at 40 and 65 degrees. These properties were essentially similar to those of the enzymes from mesophilic and thermophilic bacteria. The enzyme existed in two forms with different molecular sizes, 1.5-5 X 10(6) and 2 X 10(5) daltons, at pH 7.0 and at temperatures below 40 degrees. The larger component disaggregated into the small one at pH 8.5 or above, at temperatures above 50 degrees or in the presence of isoleucine and valine.

Namiko Muramatsu

Papers

Studies on an ATPase of thermophilic bacteria. I. Purification and properties.

Some catalytic and molecular properties of threonine deaminase from Bacillus stearothermophilus.