Plant @entity2453 reductase(HMGR; EC 1.1.1.34) and @entity969 - @entity1391 synthase (SPS; EC 2.4.1.14) and synthetic peptides designed from the known phosphorylation sites of plant HMGR (SAMS*: KSHMKYNRSTKDVK), @entity35 @entity6625 carboxylase (SAMS: HMRSAMSGLHLVKRR), @entity2772 SPS (SP2: GRRJRRISSVEJJDKK), and @entity2772 @entity2125 : @entity1507 reductase (NR6: GPTLKRTASTPFJNTTSK) were used to characterize kinase activities from cauliflower ( @entity5598 . ) inflorescences. The three major peaks of protein kinase activity resolved by anion-exchange FPLC are homologs of those observed previously in @entity2772 leaves and thus are designated PKI, PKIV, and PKIII, listed in order of elution. PKIV was the most active in terms of phosphorylation and inactivation of recombinant Nicotiana HMGR and was also strictly @entity141 dependent. The novel aspects are that PKIII has not been detected in previous cauliflower studies, that SAMS* is a more specific peptide substrate to identify potential HMGR kinases, and that the major HMGR kinase in cauliflower is @entity141 dependent. Of the three major kinases that phosphorylated the SP2 peptide only PKI (partially @entity141 sensitive) and PKIII ( @entity141 insensitive) inactivated native @entity2772 leaf SPS. Cauliflower extracts contained endogenous SPS that was inactivated by endogenous kinase(s) in an @entity855 -dependent manner and this may be one of the substrate target proteins for PKI and/or PKIII. The substrate specificity of the three kinase peaks was studied using synthetic peptide variants of the SP2 sequence. All three kinases had a strong preference for peptides with a basic residue at P-6 (as in SP2 and SAMS*; SAMS has a free @entity1472 terminus at this position) or a Pro at P-7 (as in NR6). This requirement for certain residues at P-6 or P-7 was not recognized in earlier studies but appears to be a general requirement. In plant HMGR, a conserved His residue at P-6 is involved directly in catalysis and this may explain why substrates reduced HMGR phosphorylation in vitro.

@entity2453 reductase kinase and @entity969 - XXXX synthase kinase activities in cauliflower florets: @entity141 dependence and substrate specificities.

@entity2125 :: ('MESH:D009243', 'Chemical') :: ['NADH'] @entity1472 :: ('CHEBI:46882', 'Chemical') :: ['amino'] @entity35 :: ('10116', 'Species') :: ['rat'] @entity2772 :: ('3562', 'Species') :: ['spinach'] @entity141 :: ('CHEBI:29108', 'Chemical') :: ['Ca2+'] @entity1507 :: ('CHEBI:48107', 'Chemical') :: ['nitrate'] @entity5598 :: ('3712', 'Species') :: ['Brassica oleracea L'] @entity969 :: ('MESH:D013395', 'Chemical') :: ['sucrose'] @entity1391 :: ('CHEBI:26020', 'Chemical') :: ['phosphate'] @entity2453 :: ('MESH:C008047', 'Chemical') :: ['3-hydroxy-3-methylglutaryl-CoA'] @entity6625 :: ('MESH:D000105', 'Chemical') :: ['acetyl-CoA'] @entity855 :: ('MESH:D000255', 'Chemical') :: ['ATP']
@entity1391 :: (CHEBI:26020,Chemical) :: ['phosphate']
