Posttranslational Modification Enzymes Research Articles

Relationship between genetic variation in thermal stability and electrophoretic mobility of mouse beta-galactosidase.

We have examined the relationships between the genetic determinants for mouse beta-galactosidase heat stability and electrophoretic mobility, in order to clarify previous reports indicating that a variation for enzyme heat stability is restricted to kidney while that for electrophoretic mobility is expressed in all tissues. We find that the two phenotypes show concordant strain distributions and cosegregate in genetic crosses. In contrast to a previous report, the thermal stability variation is expressed in all tissues, although the absolute rate of enzyme inactivation is tissue specific. The evidence supports the notion that a single beta-galactosidase structural locus is expressed in all tissues and that the differences in enzyme stability between tissues results from posttranslational enzyme modification.

Posttranslational modifications of enzymes.

This chapter describes enzyme alterations in some selected systems. The isocitrate lyase from old Turbatrix aceti (T. aceti) consists of a mixture of active and inactive molecules. The nematode T. aceti, the eye lens, and red blood cells are the systems that allow recognition of the most frequent and unequivocal postsynthetic changes in enzymes. G6PD shows two types of modifications: (1) a nonproteolytic lowering of the isoelectric pH and (2) a limited proteolysis of the COOH-terminal end, which takes place in the red blood cells. Aldolase undergoes a specific deamidation. Changes in enzyme level and properties can be because of changes in rates of proteolysis. Salivary amylase in humans is present as multiple isozymes, which is derived from a single gene product through posttranscriptional modifications. The lens of the eye is a very peculiar organ in many respects. It is a nonvascularized tissue, receiving nutrients from aqueous and vitreous humors. It is an organ of choice in the study of some aspects of postsynthetic changes in proteins.