Abstract
In the thyroid gland of cat and pig, combined formaldehyde-ozone treatment induces a strong greenish yellow fluorescence (maximal excitation/emission, 370/510 mµ) in cells identified as C cells by argyrophil staining. With the formaldehyde-ozone treatment, authentic tryptamine as well as tryptophyl peptides in protein droplet models gave a similar, strong fluorescence. Combined formaldehyde-HCl treatment gave only moderate C cell fluorescence. With this treatment the fluorescence yield of tryptophyl peptides in protein droplet models was low, whereas that of tryptamine was high (of the same magnitude as after formaldehyde-ozone). Chemical analysis failed to reveal tryptamine in extracts of thyroid glands. Together, the microspectrofluorometric and chemical results indicate that the fluorogenic compound in the C cells of cat and pig is a tryptophyl peptide rather than tryptamine.