鸡蛋果幼叶细胞质丙酮酸激酶的调节特性

Regulatory Properties of Cytosolic Pyruvate Kinase from Young Leaves of Passiflora edulis

鸡蛋果幼叶ＰＫｃ的Ｋｍ（ＰＥＰ）为０．０３７ｍｍｏｌ／Ｌ，Ｋｍ（ＡＤＰ）为０．０５ｍｍｏｌ／Ｌ，与成长叶相同。幼叶ＰＫｃ的效应物与成长叶的有较大差异，草酸和Ｃａ２＋对幼叶ＰＫＣｃ抑制机制与成长叶相同，但亲和力不同，这可能反映了酶的非活性部位具有不同的构象。

On the basis of a previous report on pyruvate kinase(PKc,EC 2.7.1.40) in mature leaves of passiflora edulis(Guo and Li 1993), this poper reports the regulatory properties of PKc from young leaves of the same Plant.The PKc from young leaves of P.edulis exhibited a Michaelis-Menten type kinetics for PEP and ADP,K.(PEP)=0.037 mmol/L,Km (ADP)=0.05mmol/L,which was the same as that from mature leaves(Fig.1).Some metabolites,such as Asp,Asn,malate,which activated PKc from mature leaves,had no effect on PKc from young leaves;α-ketoglutarate,which activated PKc from mature leaves,had inhibitory effect on PKc from young leaves. Fumarate, which did not affect PKc activity in mature leaves,inhibited PKc in young leaves.ATP slightly inhibited PKc in young leaves and had no effect at its physiclogical concentration,whereas it inhibited PKc Potently in mature leaves.These results indicated that differences in regulatory Properties existed between PKc in mature leaves and that in young leaves,which might be due to the difference in con formation in a part of the enzyme molecule other than the active site (Table 1,Guo and Li 1993).Oxalate showed a competitive inhibition of PKc in young leaves with respect to PEP (Ki=0.174 mmol/L)and a non-competitive one with respect to ADP(Ki=7.9 mmol/L)(Fig.2).α-ketoglutarate was a mixed-type inhibitor of PKc in young leaves with respect to PEP(Ki=3 mmol/L,K' i=12.2 mmol/L ) and non-competitive one with respect to ADP(Ki=9.77mmol/L)(Fig.3).Absolute requirement of Mg2+ for the maintenance of the structure of PKc was observed. PKc was inactive when Mg2+ was omitted during its purification from young leaves.Ca2+ inhibition of PKc was noncompetitive with respect to ADP,and anti-competitive with respect to PEP,but was competitive with respect to Mg2+(Ki=0.1 mmol/L)(Fig.46).The degree of inhibition was dependent on Mg2+ concentrations,and the PKc activity was regulated by the[Ca2+]/[Mg2+] ratio(Fig.7).