Translation activating enzymes

This constitutive, post-translationally activated enzyme enables plant cells to respond very rapidly to metal ions entering the cell. 

Many secretory proteins—e. g., pancreatic ribonuclease (RNAse see p. 74)—contain several disulfide bonds that are only formed oxidatively from SH groups after translation. The eight cysteine residues of the RNAse can in principle form 105 different pairings, but only the combination of the four disulfide bonds shown on p. 75 provides active enzyme. Incorrect pairings can block further folding or lead to unstable or insoluble conformations. The enzyme protein disulfide iso-merase [1] accelerates the equilibration between paired and unpaired cysteine residues, so that incorrect pairs can be quickly split before the protein finds its final conformation. 

There are some important limitations to the expression array approach. Since this analysis examines only the transcriptome, it fails to identify the important regulatory points at the level of translation and enzyme activity [29], in addition to the processes of protein protein interaction. Currently, the expression arrays do not address the issue of alternative splicing, but there are new generations of arrays being produced to examine these events. 

Some cells that lack telomerase activity, on the other hand, still have a high level of hTERT transcription. In these cases, regulation at the level of alternative splicing leads to skipping of exons that encode reverse transcriptase function, so any translation product would not give an active enzyme [47]. 

Observed increases in the endogenous activity of an enzyme may result from transcriptional activation of the corresponding gene, post-transcriptional processing of existing precursors of mRNA, or post-translational activation of inactive or less active enzymes. Increases in ACC synthase activity in response to auxin [32] and wounding... 

Tyrosine hydroxylase, the rate-hmiting enzyme, is a substrate for PKA, PKC, and CaM kinase phosphorylation may increase hydroxylase activity, an important acute mechanism whereby NE and Epi, acting at autoreceptors, enhance catecholamine synthesis in response to elevated nerve stimulation. In addition, there is a delayed increase in tyrosine hydroxylase gene expression after nerve stimulation, occurring at the levels of transcription, RNA processing, regulation of RNA stability, translation, and enzyme stability. Thus, multiple mechanisms maintain the content of catecholamines in response to increased transmitter release. In addition, tyrosine hydroxylase is subject to allosteric feedback inhibition by catecholamines. 

---