The p
osttranslati
onal m
odificati
ons induced
on PKC is
ozymes as result
of their activati
on were investigated. Recipr
ocal immun
oprecipitati
ons f
oll
owed by Western bl
ot analysis dem
onstrated that all PKC is
ozymes expressed in rat hepat
ocytes are m
odified by tyr
osine nitrati
on and tyr
osine ph
osph
orylati
on in different ways up
on exp
osure
of cells t
o a direct PKC activat
or (TPA),
or t
o an extracellular ligand kn
own t
o activate PKC-dependent pathways (epinephrine). Our data dem
onstrate f
or the first time that all PKC is
ozymes are als
o dynamically m
odified by O-
linked β-
N-
acetylglucosamine (O-GlcNAc); the presence
of this m
odificati
on was c
onfirmed in part by FT-ICR mass spectr
ometry analysis. Interestingly, the O-GlcNAc m
odified Ser
or Thr were mapped at similar p
ositi
ons in several PKC is
ozymes. The bi
ochemical meaning
of these p
osttranslati
onal m
odificati
ons was investigated f
or PKC alpha and delta. It was f
ound that the PKC ph
osph
orylati
on status
of b
oth is
ozymes in tyr
osine and serine residues seems t
o regulate directly the enzyme activity since catalytic inactivati
on c
orrelate with deph
osph
orylati
on
of Ser at the C-terminus aut
oph
osph
orylati
on sites
of each PKC is
ozyme, and with an increase in the level
of tyr
osine ph
osph
orylati
on. Whereas n
one
of the
other p
osttranslati
onal m
odificati
ons sh
owed per se a direct effect in PKC delta activity, increased tyr
osine nitrati
on and O-GlcNAc m
odificati
ons c
orrelate negatively with PKC
![](http://www.sciencedirect.c<font color=)
om/scidirimg/entities/204e.gif" alt="greek small letter alpha" title="greek small letter alpha" b
order="0"> activity.