Angular 5 Observable mapping to Json array

My backend return this :

{
"FirstResponse": [
{
"MyField1": "AAA",
"MyField2": "AAAAAAA"
},
{
"MyField1": "BBB",
"MyField2": "BBBBBBB"
},
{
"MyField1": "CCC",
"MyField2": "CCCCC"
}
],
"SecondResponse": [
{
"FirstName": "FirstNameA",
"LastName": "LastNameA"
},
{
"FirstName": "FirstNameB",
"LastName": "LastNameB"
}
]
}


I'd like map FirstReponse to a variable and SecondResponse to another variable.

How can I adapt the code below ?

search(): Observable<any> {
let apiURL = `......`;
return this.http.get(apiURL)
.map(res => res.json())
}


Update : Excepted result In one variable this :

[
{
"MyField1": "AAA",
"MyField2": "AAAAAAA"
},
{
"MyField1": "BBB",
"MyField2": "BBBBBBB"
},
{
"MyField1": "CCC",
"MyField2": "CCCCC"
}
]


In a second :

[
{
"FirstName": "FirstNameA",
"LastName": "LastNameA"
},
{
"FirstName": "FirstNameB",
"LastName": "LastNameB"
}
]

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