Evidence for two dissimilar polypeptide chains in the beta 2 subunit of hexosaminidase.

Publisher Website
Google Scholar
Abstract
The major isoenzymes of human hexosaminidase [which is deficient in Tay-Sachs disease and Sandhoff disease] have the structures .alpha..beta.2 (hex A) and 2.beta.2 (hex B). Evidence is presented that the .beta.2 subunit of hex B and hex BA (the form of hex B derived from hex A) is composed of 2 nonidentical polypeptide chains, .beta.a and .beta.b. They have similar MW (25,000) but have pI [isoelectric point] values that differ by 1 unit. A 2-dimensional analytical gel electrophoresis method was used in combination with peptide mapping to compare the primary sequence structure of the 2 .beta. chains. In this method, the polypeptide chains of hex B or hex BA were first separated by isoelectric focusing in 8.5 M urea. The separated chains were subjected to partial proleolytic digestion in the stacking gel of a second sodium dodecyl sulfate4/polyacrylamide gel with subsequent separation of peptides by electrophoresis into the second gel. Partial digestion by protease V8 or papain showed that the .beta.a and .beta.b species have distinct primary structures, neither of which was similar to that of the .alpha. chain. The .beta.2 subunit of hexosaminidase probably has the structure of .beta.a.beta.b. The possibility that the distinct .beta. chains are encoded by a single gene is discussed in the light of genetic and other data.