Harker, David

The final step in complete elucidation of the three-dimensional structure of ribonuclcasc was made by researchers at the Roswell Park Memorial Institute. Buffalo. New York. This group, headed by Dr. David Harker, employed x-ray diffraction techniques. Roughly 500.000 diffraction points were recorded and the data so obtained w as fed to a computer. 

The protein crystallographer, David Harker, identified the key issue ... 

I believe it could ve happened. That would not have surprised me. It had already happened that Jerry and Isabella were members of the National Academy of Sciences and I wasn t. She became a member soon after Jerry had become a member. David Harker who promoted me for membership in the Academy, told me that Jerry had prevented my election by arguing that Herb is too mathematical. I believe that Jerry wanted to win the Nobel Prize for himself and Isabella alone but I was a thorn in their side because in the period of the 1950s, Jerry and I had co-authored several... 

He built a wonderful center for polymer science at Brooklyn Polytechnic and made the place stimulating in many ways. There were other outstanding people at Brooklyn Polytechnic, like Ewald in crystallography — he was Head of the Physics Department Fankuchen, who had worked with Bernal, and Ben Post and David Harker were other crystallographers there. 

Isomorphous replacement is now employed in the determination of the structures of biological macromolecules. These molecules crystallize with 50% or more of the crystal volume filled with solvent molecules. Murray Vernon King, working with David Harker, conceived the idea of soaking protein crystals in solutions of compounds containing a heavy atom. These heavy-atom compounds are diffused into the crystals through the solvent channels and settle on preferred sites on protein molecules. The diffraction patterns of the unperturbed crystal (described as "native ) and the heavy-atom derivative are then compared in such a way that an electron-density map for the protein results. The method of isomorphous replacement, and the manner by which it is used to derive relative phases, are described in detail in Chapter 8. 

The methods used to ensure that the Fourier summation does not give a negative electron-density map are mathematical in nature. David Harker and John Kasper in 1948 used the inequality relationships of Augustin Louis Cauchy, Hermann Amandus Schwarz, and Victor Buniakowsky [Buniakovski] (generalized to the Cauchy—Schwarz inequality) to derive relationships between the structure factors (the Harker—Kasper inequalities). These were used by David Harker. John Kasper, and Charlys Lucht to determine the structure of decab-orane, BioH, which was unknown at that time. For this study they... 

The symmetry of the Patterson function is the same as the Laue symmetry of the crystal. The Patterson function for space groups that have symmetry operations with translational components (screw axes and glide planes) has an added property that is very useful for the determination of the coordinates of heavy atoms. Specific peaks, first described b David Harker, are associated with the vectors between atoms related by these symmetry operators. These peaks are found along lines or sections (Figure 8.17). For example, in the space group P2i2i2i there are atoms at... 

To solve this vector relationship, David Harker proposed the simple graphical method shown in Figure 8.5 for determining the native protein phase nat, given /, Fnat, and Fderiv... 

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