BIOCHEMICAL STUDIES OF SALIVARY MUCIN

¹ Laboratory of Biological Chemistry of Columbia University, at the College of Physicians and Surgeons, New York City

Mucin and sodium mucinate were prepared from submaxillary glands by standard methods, with minor modifications. The resulting mucinate was totally soluble in water.

Mucin is said to be precipitated from its solutions by salts of lead and mercury, but in the biological range of concentration this does not occur.

The reaction of maximum precipitation ("isoelectric zone") of mucin by dilute acid is pH 2.95 to 2.75. Maximum precipitation can be accurately obtained, for practical analytic purposes, by titration with N/50 hydrochloric acid, added drop by drop until a drop fails to increase the turbidity.

Various methods for the quantitative determination of mucin were tried. The nature of the turbidity produced by acid precipitation, while unsuited for direct gravimetric determination after separation of the mucin, suggested nephelometry.

A described nephelometric method includes preliminary clearing of the normally turbid saliva with alkali and removal, by dialysis, of salts that interfere with precipitation. By this method added mucin can be recovered from saliva with an error of less than 4 percent.

Fifty-three analyses of "unstimulated" saliva from human subjects gave an average mucinate content of 0.25 ± 0.06 percent. A series of analyses were also made on saliva collected after various types of stimulation.

Oral relationships of the data are indicated.

In conclusion the author wishes to express his sincere thanks to Prof. William J. Gies, who initiated the work and offered valuable suggestions, and to Prof. Edgar G. Miller, Jr. for his constant and generous cooperation in the research. He also gratefully acknowledges the assistance of Jessica P.Leland and Arthur B. Roth in the determinations of the mucinate content of "unstimulated" saliva.