Comparison of Glycogen Phosphorylase Kinases of Various Rat Tissues1

Abstract

Glycogen phosphorylase kinases in soluble fractions of various rat tissues were examined for the pH 6.8/8.5 activity ratio, Ca2+-dependency, activation by cyclic AMP-dependent protein kinase (protein kinase A), and reactivity with anti-skeletal muscle phosphorylase kinase serum. The enzymes could be divided into at least two major groups; muscle and liver types. The muscle type, that has a low value of pH 6.8/8.5 activity ratio, is highly dependent on Ca2+, markedly activated by protein kinase A, and strongly inhibited by the antiserum. Inversely, the liver type, that has a high value of pH 6.8/8.5 activity ratio, is poorly dependent on Ca2+, not activated by protein kinase A, and weakly inhibited by the antiserum. The enzymes from heart and skeletal muscle were similar and belonged to the former entity. Whereas, the enzymes from liver, kidney, spleen, lung, and testis appeared to belong to the latter entity. The enzyme from brain apparently differs from these entities, and seems to be an intermediate type or a hybrid of the two.

I/Lyn mouse phosphorylase kinase deficiency: mutation disrupts expression of the alpha/alpha'-subunit mRNAs.

“…In this case the absence of a mRNA in liver would mean that its abundance is normally too low to detect and is significantly lower than that seen in heart. This is unlikely given that the abundance of the phosphorylase kinase protein is approximately equal in liver and heart (37,38).…”

The regulation of glycogenolysis in the brain

“…In contrast to mPhK, very little is known about the structure, activity, and regulation of bPhK. The PhK activity in brain lysates is ϳ7% that of muscle, normalized by protein concentration (24). It should be noted, however, that these lysates would represent glial, neuronal, endothelial, and smooth mus-cle cells.…”

“…The mass of bPhK does not appear to have been estimated; however, it most likely has the same quaternary structure as mPhK and lPhK, because all four subunits are expressed in brain (25). Moreover, both Ca 2ϩ and PKA have been shown to activate bPhK in lysates, further suggesting a similar subunit composition and regulation of the PhK from various tissues, although there were significant qualitative differences in the activation profiles (24). It should be noted, however, and is detailed in subsequent sections, transcripts of the muscle isoforms of the ␣, ␤, and ␥ subunits are all found in brain, but the brain additionally has transcripts corresponding to the ␥ subunit isoform associated with liver and a ␤ subunit isoform that predominates in brain.…”

Κιναση Της Φωσφορυλασησ:μερικος Καθαρισμος,κυτταρικος Και Υποκυτταρικος Εντοπισμος Του Ενζυμου Στο Νευρικο Ιστο

“…Αξίζει όμως να σημειωθεί ότι η δραστικότητα αυτή είναι δεύτερη κατά σειρά μετά τη δραστικότητα των σκελετικών μυών, σε μία σειρά ιστών που μελετήθηκαν, όπως σκελετικοί μύες, καρδιά, εγκέφαλος, ήπαρ, νεφρά, σπλήνα, πνεύμονες και όρχεις (Taira et al, 1982). Μέχρι σήμερα δεν έχει επιτευχθεί καθαρισμός του ενζύμου.…”