Pantothenate kinase regulation of the intracellular concentration of coenzyme A

Pantothenate kinase (PanK) is the key regulatory enzyme in the CoA biosynth etic pathway in bacteria and is thought to play a similar role in mammalian cells. We examined this hypothesis by identifying and characterizing two m urine cDNAs that encoded PanK. The two cDNAs were predicted to arise from a lternate splicing of the same gene to yield different mRNAs that encode two isoforms (mPanK1 alpha and mPanK1 beta) with distinct amino termini. The p redicted protein sequence of mPanK1 was not related to bacterial PanK but e xhibited significant similarity to Aspergillus nidulans PanK. mPanK1 alpha was most highly expressed in heart and kidney, whereas mPanK1 beta mRNA was detected primarily in liver and kidney. Pantothenate was the most abundant pathway component (42.8%) in normal cells providing clear evidence that pa ntothenate phosphorylation was a rate-controlling step in CoA biosynthesis. Enhanced mPanK1 beta expression eliminated the intracellular pantothenate pool and triggered a 13-fold increase in intracellular CoA content. mPanK1 beta activity in vitro was stimulated by CoA and strongly inhibited by acet yl-CoA illustrating that differential modulation of mPanK1 beta activity by pathway end products also contributed to the management of CoA levels. The se data support the concept that the expression and/or activity of PanK is a determining factor in the physiological regulation of the intracellular C oA concentration.