Lg. Meszaros et al., SARCOPLASMIC RETICULUM-ASSOCIATED AND PROTEIN-KINASE C-REGULATED ADP-RIBOSYL CYCLASE IN CARDIAC-MUSCLE, Biochemical and biophysical research communications, 234(1), 1997, pp. 252-256
Two types of ADP-ribosyl cyclase activity were distinguished in dog an
d rat cardiac muscles by measuring the enzymatic conversion of NGD (as
an NAD analog) into the fluorescent product cyclic GDP-ribose in card
iac muscle subcellular fractions. Both types of activity were confined
to membrane fractions isolated from microsomes by sucrose gradient ce
ntrifugation. One of the activities co-purified with fractions that we
re enriched in sarcolemma (SLM), as evidenced by immunodetection of th
e dihydropyridine receptor, while the other activity was found to co-p
recipitate with the sarcoplasmic reticulum (SR), that was identified o
n the basis of its immune-staining with a ryanodine receptor monoclona
l antibody. In certain aspects, the plasma membrane-bound ADP-ribosyl
cyclase activity resembled the characteristics of CD38 or CD38-like pr
oteins: it was sensitive to thiols and lectins and was recognized by a
monoclonal anti CD38 antibody. The SR enzyme had apparently distinct
properties, as it was insensitive to both thiols and lectins and was n
ot recognized by the CD38 antibody. In addition, the SR-associated ADP
-ribosyl cyclase was inhibited by endogenous protein kinase C (PKC)-de
pendent phosphorylation in both dog and rat cardiac SR. The PKC-modula
ted SR ADP-ribosyl cyclase we describe here might be a principal compo
nent of the signal transduction machinery that is responsible for regu
lation of the intracellular levels of cADPR. (C) 1997 Academic Press.