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Recent studies of acetylcholinesterase (AChE) and related enzyme systems at the myoneural junction are reviewed primarily from the ultrastructural cytochemical point of view. The four most prevalent methods used to determine localization of AChE ultrastructurally are: (a) a hexazotized pararosaniline diazo coupling method, (b) a thiolacetic acid method and modifications, (c) a thiocholine method and modifications and (d) osmioph.ilic thiolester methods. After an initial discussion of key questions germaine to the subject matter and a short summary to introduce ultrastructural considerations, the principles upon which the above four groups of methods are based are described with a critical evaluation of their advantages and disadvantages. Such characteristics as specificity, localization, penetration, ascertaining bound and unbound enzymes, dangers of nonenzymatic reactions and contrast in the electron microscope from the primary reaction product are detailed and compared for each method.

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Examines the use of zone melting to purify pharmaceuticals.