Phosphates and other enzymes considered in relation to active transport and the function of fibrous protein structures

Abstract

Many students of active transfer of molecules through membranes have postulated that the transfer is mediated with the aid of enzymes, particularly phosphatases. Verzar and Wilbrandt and Lastz in particular emphasized this point. However, all theories of this nature imply that certain enzyme systems are localized in particular regions of cells. Until quite recently it was not possible to determine the site of enzymes with sufficient precision to permit experimental investigation of the postulated localizations. The first experiments on the localization of alkaline phosphatase were carried out by Robison (1923). In these experiments tissue sections were exposed to a solution containing a phosphate ester and calcium. Where phosphatase was present phosphate ion was liberated from ester by enzymic hydrolysis, and precipitated in the section as calcium phosphate. Gomori (1939) and Takamatsu (1939) showed that the precipitate so formed was deposited in certain cellular sites only, and claimed that these sites were the actual sites of enzymic activity. Subsequent investigations have shown that this claim is, in part, justified. Before such claims can be accepted critical examination of techniques is essential. Answers must be provided to the following questions: ( а ) How much enzyme is destroyed during the preparation of tissue sections, and if there is destruction, does it occur unequally at different sites? ( b ) Is the precipitate formed at the actual site of enzymic activity, or is it formed at sites having a special affinity for the precipitate? ( c ) Is the enzyme in a tissue section in its physiologically normal position? ( d ) Is the substrate for the enzyme able to penetrate to all sites of enzyme activity?