Abstract
The interaction of soluble tyrosine hydroxylase with isolated chromaffin granule membranes was studied. The incubation of the granule membranes with the soluble fraction in the mixture that may approximate the intracellular environment of the resting cell resulted in a marked increase in the enzyme activity recovered in the membrane fraction, and enzyme activity precipitated with the granule membranes was increased according to incubation time and dependent on amounts of both the granule membranes and soluble fraction. The association of the soluble enzyme with the granule membranes was reversible and specific, whereas a decrease in activity of the soluble enzyme was observed when the soluble fraction was incubated with the granule membranes in the mixture in which association of the soluble enzyme with the granule membranes might occur. These results seem to indicate that activity of the soluble enzyme is presumably modulated by the granule through association of the soluble enzyme with the surface of the granule, thus suggesting that interaction between tyrosine hydroxylase and the chromaffin granule may play a possible role in regulation of catecholamine biosynthesis as a consequence of modulating activity of the rate-limiting enzyme within the cell.
Highlights
I N VITRO STUDIES ONASSOCIATION OF SOLUBLE ENZYME WITH GRANULE MEMBRANES AND ALTERATION IN ENZYME ACTIVITY*
The incubation of the granule membranes with the soluble fraction in the mixture that may approximate the intracellular environment of the resting cell resulted in amarked increase in the enzyme activity recovered in the membrane fraction, and enzyme activity precipitated with the granule membranes was increased according to incubation time and dependent on amounts ofboth the granule membranesand soluble fraction
The association of the soluble enzyme with the granule membranes was reversible and specific, whereas a decrease in activity of the soluble enzyme was observed when the soluble fraction was incubated with the granule membranes in the mixture in which association of the soluble enzyme with the granule observations suggest that tyrosine hydroxylase recovered in the particulate fraction may originally be a soluble form within the cell [11, 12]
Summary
I N VITRO STUDIES ONASSOCIATION OF SOLUBLE ENZYME WITH GRANULE MEMBRANES AND ALTERATION IN ENZYME ACTIVITY*. These results seem to indicate ies seem to suffer from redistribution of proteins as well as that activity of the soluble enzyme is presumably mod- other components during fractionationor fixation procedures, ulated by the granule through association of the soluble it hasproven difficult to study such loose associations between enzyme with the surface of the granule, suggesting that interaction between tyrosine hydroxylase and the chromaffin granule may play a possible role in regulation of catecholamine biosynthesis as a consequence of modulating activity of therate-limiting enzyme within the cell. It has been shown that aggregation and adsorption of the soluble enzyme on the surface of particles readily occur in the homogenization and purification procedures These that tyrosine hydroxylase may be localized ianssociation with the surface of subcellular organelles, possibly chromaffin granule, within the adrenal chromaffin cell [16].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
