= John Cowdery Kendrew
{c}
{tag=Chemistry author}
{title2=1917-1997}
{wiki}
= John Kendrew
{c}
{synonym}
= J. C. Kendrew
{c}
{synonym}
\b[John Cowdery Kendrew] helped establish how <X-ray crystallography> can reveal the three-dimensional arrangement of a <protein>. Nobel's primary nomination archive names John Cowdery Kendrew, also identifying J. C. Kendrew in its award-sharing comment.<John Cowdery Kendrew in the Nobel nomination archive>[1962 nomination64-0,nominee2 and Comments]{ref}
His team's1960 <myoglobin> paper presented a <Fourier analysis> at2-angstrom resolution. Its opening recalls how earlier phase determination compared native crystals with <heavy-atom derivatives> containing localized mercury or gold sites. Such comparisons supply information missing from a simple measurement of <diffraction intensity>.<Structure of Myoglobin: A Three-Dimensional Fourier Synthesis at 2 Å. Resolution by J. C. Kendrew and others>[Page422,opening discussion of earlier phasing and the2Å analysis]{ref}
An original one-dimensional example explains that <phase problem>. Write a periodic <electron density> using <Fourier series> coefficients $F_k$. The two positive densities
$$
\rho_+(x)=3+\cos x+\tfrac12\cos2x,\qquad
\rho_-(x)=3+\cos x-\tfrac12\cos2x
$$
have $F_0=3$, $F_{\pm1}=1/2$ and $F_{\pm2}=\pm1/4$, with the final sign distinguishing them. Their squared coefficient magnitudes are identical:9 for mode zero,1/4 for modes $\pm1$ and1/16 for modes $\pm2$. The relative phase of the second harmonic has changed while the first harmonic is fixed. Thus equal intensities need not identify one density.
\Image[/diffraction-phase-ambiguity.png]
{title=Different positive model densities can have the same squared <Fourier coefficient> magnitudes}
{description=Original one-dimensional mathematical example, not a measured protein diffraction pattern. The sign of the second harmonic differs while the first harmonic is unchanged, so the density shapes differ despite equal mode intensities.}
The myoglobin experiment was more demanding than this toy calculation, but the distinction motivates its chemical strategy: modifying crystals at known heavy-atom sites changes their scattering in a way that constrains phase information. Reconstructing an <electron density> map therefore requires both measured diffraction and a justified phase-determination method, rather than treating the recorded spots as a direct photograph of the molecule.
\Image[https://mrclmb.ac.uk/wp-content/uploads/1962_Kendrew-John_01040_14_c-MRC_LMB.jpg]
{title=John Kendrew, named portrait from the MRC Laboratory of Molecular Biology Image Bank}
{height=300}
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