THE EFFECT OF BORIC ACID ON THE REACTION OF LEAD TETRAACETATE WITH POLYSACCHARIDES IN FILMS AND TISSUE SECTIONS

1. A preferential reaction of lead tetraacetate and boric acid with vic-glycols having the cis-configuration was investigated with a view to developing a more specific histochemical method for polysaccharides and glycoproteins. 2. With this objective, the effect of boric acid on the oxidation of polysaccharides and glycoproteins by lead tetraacetate in glacial acetic acid, as revealed by subsequent staining with aldehyde reagents, was studied in films of purified polysaccharides incorporated in gelatine (`Model' Preparations) and in tissue sections containing the same or similar compounds. 3. The staining intensity of `Model' Preparations was measured quantitatively by means of a recording microdensitometer. 4. In `Model' Preparations the reactions of galactogen, mannan, and alginic acid, all having reactive adjacent cis-hydroxyl groups, were compared with those of glycogen, and a partially hydrolysed dextran, both assumed to contain only reactive adjacent trans-hydroxyls. In parallel experiments sections of the following tissues were studied: albumin gland of Helix pomatia; liver, tracheal cartilage, thyroid gland, and mixed pharyngeal glands of the mouse. 5. Boric acid partially blocked the oxidation of mannan and galactogen but the oxidation of alginic acid was unaffected. Thus, while boric acid could exert its effect irrespective of whether the reactive hydroxyls were its a single chain or in branch chains, the character of the groups in close proximity to the reactive hydroxyls greatly influenced the reaction. 6. At room temperature lead tetraacetate oxidized glycogen and dextran much less readily than either mannan, galactogen, or alginic acid. Whereas boric acid had a slight blocking affect on the oxidation of glycogen at room temperature, the oxidation of dextran was probably not significantly affected. However, at 50°C. the blocking effect of boric acid was marked in the case of glycogen and appreciable its the case of dextran. This result was unexpected. 7. Galactogen in the albumin gland and glycogen in the liver reacted similarly to the purified materials. The oxidation of cartilage matrix (A) and material present in mucous alveoli (B) of the pharyngeal glands was partially (A) or completely (B) blocked by boric acid, but the reaction of basement membranes and serous alveoli was not affected; nor was the vigorous reaction of thyroid colloid. 8. In `Model' Preparations it was demonstrated that boric acid competed with lead tetraacetate for reactive groups and protected them from oxidation; but, because of adsorption of lead tetraacetate, it could not be shown unequivocally that in the presence of boric acid less lead tetraacetate was consumed in the oxidation of polysaccharide. 9. The apparently anomalous reactions of glycogen and dextran with boric acid may be due to complex formation with pairs of cis-hydroxyl groups, which, though in the same hexose radical, are not adjacent. Despite this, it is claimed that the use of lead tetraacetate its combination with boric acid is a valuable histochemical technique for revealing the presence of reactive adjacent cis-hydroxyl groups in polysaccharides and glycoproteins.