Myristoyl-CoA

Look al the catabolism of my fistic acid shown in Figure 29.4 to see the overall results of the /3-oxidation pathway. The first passage converts the 14-carbon myristoyl CoA into the 12-carbon lauroyl CoA plus acetyl CoA, the second passage converts lauroyl CoA into the 10-carbon caproyl CoA plus acetyl CoA, the third passage converts caproyl CoA into the 8-carbon capryloyl CoA, and so on. Note that the final passage produces two molecules of acetyl CoA because the precursor has four carbons. 

Following removal of one acetyl-CoA unit from palmitoyl-CoA, the coenzyme A thioester of the shortened fatty acid (now the 14-carbon myristate) remains. The myristoyl-CoA can now go through another set of four /3-oxidation reactions, exactly analogous to the first, to yield a second molecule of acetyl-CoA and lauroyl-CoA, the coenzyme A thioester of the 12-carbon laurate. Altogether, seven passes through the j8-oxidation sequence are required to oxidize one molecule of palmitoyl-CoA to eight molecules of acetyl-CoA (Fig. 17-8b). The overall equation is... 

Myristoyl-CoA Protein /V-Myristoyltransferase and Myristoyl-CoA Binding Protein from Bovine Cardiac Muscle... 

Abstract Protein myristoylation refers to the cotranslational addition of a myris-toyl group to an amino-terminal glycine residue of a protein by the enzyme IV-myristoyltransferase (NMT). The myristoylation reaction depends on the availability of the cellular pools of coenzyme A and myristate and their subsequent formation of myristoyl-CoA, the substrate of NMT. In this review, we discuss NMT and myristoyl-CoA binding protein from bovine cardiac muscle which was carried out in our laboratory. 

Our laboratory has provided significant contributions in the area of myristoyla-tion. We discovered and purified the myristoyl-CoA binding protein (MCBP) from bovine cardiac muscle (Raju and Sharma 1997). In cardiac tissues there is a high level of cAMP-dependent protein kinase expression whose catalytic subunit is myristoylated (Carr et al. 1982). The catalytic subunit of cAMP-dependent protein kinase and the beta subunit of calcineurin are myristoylated proteins localized in the cytoplasm (Selvakumar et al. 2006, 2002 Rajala et al. 2000 Johnson et al. 1994 Carr et al. 1982 Aitken et al. 1982). Recently it has been shown that dephosphorylation of the catalytic subunit of myristoylated and nonmyristoylated cAMP-dependent protein kinase at Thr-197 by cellular protein phosphatase and protein... 

Fig. 17.4 (A) Inhibition of MCBP by NIP71. (B) Deacylation of protein-myristoyl-CoA complex. For details see Raju et al. (1997).

We examined whether the protein-myristoyl-CoA complex could be inhibited by NIP71. The results indicated that NIP71 did not inhibit the formation of com-plexation between MCBP and myristoyl-CoA (Figure 17.4A). On the other hand,... 

Purified MCBP was incubated with [l-14C]myristoyl-CoA in separate tubes and aliquots were removed at selected times. At time 10 min, cytosolic fraction was added to one tube and buffer was added to the other. Aliquots were removed at selected times up to 120 min. The vial which did not contain added cytosol exhibited the formation of a protein-myristoyl-CoA complex, while the tube which contained added cytosol exhibited deacylation (Figure 17.4B). These results suggest that the cytosolic fraction may contain thioesterases/proteinases which could modulate the acylation reaction in vivo (Raju and Sharma 1997). The absence of acyl-complex formation in the cytosol could be due to the presence of either esterases or pro-teinases. It has been reported that porcine phospholipase A contained thioesterase and deacylase activities (Nocito et al. 1996). 

Duronio, R. J., Reed, S. I., and Gordon, J. I. 1992. Mutations of human myristoyl-CoA protein N-myristoyltransferase cause temperature-sensitive myristic acid auxotrophy in Saccharomyces cerevisiae. Proc. Natl. Acad. Sci. USA 89 4129—4133. 

King, M. 1., and Sharma, R. K. 1992. Demonstration of multiple forms of bovine brain myristoyl CoA protein N-myristoyl transferase. Mol. Cell. Biochem. 113 77-81. 

Mcllhinney, R. A., McGlone, K., and Willis, A. C. 1993. Purification and partial sequencing of myristoyl-CoA protein N-myristoyltransferase from bovine brain. Biochem. J. 290 405 110. 

Ntwasa, M., Egerton, M., and Gay, N. J. 1997. Sequence and expression of Drosophila myristoyl-CoA protein N-myristoyltransferase evidence for proteolytic processing and membrane localisation. J. Cell Sci. 110 149-156. 

Raju, R. V., and Sharma, R. K. 1997. Demonstration and purification of a myristoyl-CoA binding protein from bovine cardiac muscle. Life Sci. 60 2145-2153. 

Rundle, D. R., Rajala, R. V., and Anderson, R. E. 2002. Characterization of Type I and Type II myristoyl-CoA protein N-myristoyltransferases with the Acyl-CoAs found on heterogeneously acylated retinal proteins. Exp. Eye Res. 75 87-97. 

Figure 19.6 indicates the oxidation of palmitoyl-CoA to myristoyl-CoA with the production of an acetyl-CoA molecule. The myristoyl-CoA molecule can undergo another oxidative cycle, and so on. Note that the /3-hydroxyacyl-CoA dehydrogenase is specific for the l isomer of /3-hydroxyacyl-CoA. Also note that at least three acetyl-CoA dehydrogenases exist, one favoring short-chain fatty acids, another intermediate-length fatty adds, and the third long-chain fatty adds. 

Fig. 13-5 Metabolic pathway of /3-oxidation removal of the first two carbon units of a fatty acid. If the acyl-CoA (1) is palmitoyl-CoA (Ci6 o)> then acyl-CoA (2) is myristoyl-CoA (Ci4 0). Hence, the complete /3-oxida-tion of palmitoyl-CoA requires seven such cleavages and produces eight molecules of acetyl-CoA. The numbers to the left of the arrows correspond to the numbered reactions in Table 13.1.

FIGURE 7.5 Reaction catalyzed by myristoyl-CoA protein IV-myristoyltransferase in eukaryotic cells. (Source Pennise, C.R. et al. 2002. Anal. Biochem. 300, 275. Reprinted with permission from Elsevier.)... 

Lodge, J.K. et al. 1994. Targeted gene replacement demonstrates that myristoyl-CoA protein jV-in y ri stoy I Iran s ferase is essential for viability of Cryptococcus neoformans. Proc. Natl. Acad. Sci. USA 91, 12008-12012. 

Oxopentadecyl)-CoA, a nonhydrolyzable analog of myristoyl-CoA, is a potent inhibitor of myristoyl-CoA-protein N-myristoyl-transferase. J. Med. Chem. 1989 32 1665-1667. 

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