The spectral light absorption of the in vitro periodic acid-Schiff reactions of 4 purified pituitary hormones is described. The absorption spectra present a maximum between 560 and 565 mµ. The color developed conforms with Beer's law for the ranges of concentration examined. The different hormones exhibit different chromogenicity per unit of biological activity: the color produced by 1 unit of FSH is equivalent to approximately 2 of TSH, 4 of LH, and 30 of ACTH. Microspectrophotometric measurements of the PAS-positive structures in histological sections of the human pituitary give absorption curves with shapes similar to those obtained in vitro, although quantitative differences exist. It is concluded that under the proper experimental conditions microspectra of the pituitary structures might, in the future, prove to give a quantitative measure of aldehyde groups generated from glycoprotein tropins by periodate oxidation.

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