Measurement of Lp-PLA

1. An assay method comprising:

allowing an enzyme to hydrolyze lyso-platelet-activating factors (lyso-PAFs) in the presence of platelet-activating factors (PAFs) to thereby produce choline by hydrolysis of the lyso-PAFs without producing choline by hydrolysis of the PAFs, the PAFs being represented by General Formula I below:

and

measuring the amount of choline produced,

wherein:

R 1 is a linear or branched, saturated or partially unsaturated higher hydrocarbon group;

R 2 is a linear lower alkyl group; and

X is —C(O)—, —CH 2 — or —CH═CH—;

the lyso-PAFs being represented by General Formula II below:

wherein R 1 and X are defined as in General Formula I, and

the enzyme being a protein according to any of (a) to (c) below:

(a) a protein comprising SEQ ID NO: 1 or 9;

(b) a protein comprising SEQ ID NO: 1 or 9 and having 1 to 9 amino acids deleted, substituted or added therein, and having phospholipase D-like (PLD) activity against lyso-PAF but no PLD activity against PAF; or

(c) a protein having at least 90% sequence identity to SEQ ID NO: 1 or 9, and having PLD activity against lyso-PAF but no PLD activity against PAF.

2. The method according to claim 1 , wherein the measuring comprises directly measuring the amount of choline produced.

3. The method according to claim 1 , wherein the measuring comprises: reacting the choline with choline oxidase to produce hydrogen peroxide; and measuring the amount of hydrogen peroxide produced.

4. A method for measuring lipoprotein-associated phospholipase A2 (Lp-PLA 2 ) activity in a sample containing Lp-PLA 2 ,

the method comprising the following steps (A) to (C):

(A) converting platelet-activating factors (PAFs) represented by General Formula I below:

wherein:

R 1 is a linear or branched, saturated or partially unsaturated higher hydrocarbon group;

R 2 is a linear lower alkyl group; and

X is —C(O)—, —CH 2 — or —CH═CH—,

into lyso-PAFs represented by General Formula II below:

wherein R 1 and X are defined as in General Formula I,

by reacting the PAFs with the Lp-PLA 2 in the sample;

(B) hydrolyzing the lyso-PAFs produced in step (A) with an enzyme that is a protein according to any of (a) to (c) below to obtain hydrolysate:

(a) a protein comprising SEQ ID NO: 1 or 9,

(b) a protein comprising SEQ ID NO: 1 or 9 and having 1 to 9 amino acids deleted, substituted or added therein, and having phospholipase D-like (PLD) activity against lyso-PAF but no PLD activity against PAF, or

(c) a protein having at least 90% sequence identity to SEQ ID NO: 1 or 9, and having PLD activity against lyso-PAF but no PLD activity against PAF; and

(C) measuring Lp-PLA 2 activity in the sample by utilizing a quantitative change attributable to the hydrolysate obtained in step (B) as an indicator.

5. The method according to claim 4 , wherein the quantitative change in step (C) is a change in the amount of hydrolysate choline.

6. The method according to claim 5 , wherein the step (C) also comprises a following step (C-1) as a method of measuring the change in the amount of choline:

(C-1) reacting choline with choline oxidase to produce hydrogen peroxide.

7. The method according to claim 6 , wherein the step (C) also comprises a following step (C-2):

(C-2) measuring the amount of hydrogen peroxide produced in the step (C-1) by a colorimetric method using a chromogenic reagent.

8. The method according to claim 4 , further comprising a following step (D) prior to the step (A):

(D) removing the choline in the sample.

9. The method according to claim 8 , wherein the step (D) is removing the choline in the sample by utilizing choline oxidase.

10. The method according to claim 4 , wherein R 2 is a methyl group.

11. The method according to claim 4 , wherein R 1 is independently selected from C 15 and C 17 linear alkyl groups.

12. The method according to claim 4 , wherein X is —CH 2 —.

13. The method according to claim 4 , wherein X is —C(O)—.